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THE  UNIVERSITY 

OF  ILLINOIS 

LIBRARY 

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A8RIGULTURAL 
U1BARY 


Agricultural  Experiment  Station 


BULLETIN  No.  225 


NITRATE  PRODUCTION  IN  FIELD  SOILS 
IN  ILLINOIS 


BY  ALBERT  L.  WHITING  AND  WARREN  R.  SCHOONOVER 


URBANA,  ILLINOIS,  MARCH,  1920 


CONTENTS  OF  BULLETIN  No.  225 

PAGE 

INTRODUCTION 21 

Purpose  of  Investigation 23 

Effect  of  Soil  Treatment  on  Amount  of  Nitrate  Produced 24 

Influence  of  Tillage  on  Nitrate  Production 24 

The  Course  of  Nitrate  Production  in  Field  Soils 25 

Interpretation  of  Experimental  Eesults 27 

NITRATE  PRODUCTION  IN  CORN-BELT  SOILS  (NORTH  FARM  AT  URBANA) 29 

Nitrate  Nitrogen  in  Soil  Growing  Corn  in  1915,  Series  400 30 

Nitrate  Nitrogen  in  Soil  Growing  Corn  in  1916,  Series  500 32 

Value  of  Active  Organic  Matter  in  Nitrate  Production 35 

Gain  for  Phosphorus 36 

Gain  for  Limestone 36 

Nitrate  Nitrogen  in  Soil  Growing  Corn  in  1917,  Series  200 36 

Nitrate  Nitrogen  in  Soil  Growing  Corn  in  1918,  Series  300 38 

Nitrate  Nitrogen  in  Soil  Growing  Wheat  in  1915-16,  Series  200 40 

Nitrate  Nitrogen  in  Soil  Growing  Oats  in  1917,  Series  500 43 

SOME  IMPORTANT  FACTS  SHOWN  BY  DATA  FROM  THE  NORTH  FARM 45 

Corn  Crop    45 

Wheat  Crop 46 

Oat  Crop    46 

EFFECT  OF  SOIL  TREATMENT  AND  OF  CROPPING  SYSTEMS  ON  NITRATE  PRODUCTION 

(SOUTH  FARM  AT  URBANA) 47 

Influence  of  Green  Manure  as  Compared  with  Stabile  Manure 49 

Influence  of  Kaw  Rock  Phosphate 50 

Effect  of  Limestone  on  Nitrate  Production 53 

Cropping  Systems  as  Influencing  Nitrate  Production 54 

Crop  Sequence  as  Influencing  Nitrate  Production 55 

Moisture  Determinations  on  the  South  Farm 56 

SOME  IMPORTANT  FACTS  SHOWN  BY  DATA  FROM  THE  SOUTH  FARM 59 

CONCLUSIONS 60 

APPENDIX   (Methods)    62 


NITRATE  PRODUCTION  IN  FIELD  SOILS 
IN  ILLINOIS 

BY  ALBEET  L.  WHITING,  CHIEF  IN  SOIL  BIOLOGY,  AND 
WARKEN  E.  SCHOONOVEE,1  ASSOCIATE  IN  SOIL  FERTILITY 

INTRODUCTION 

The  ability  of  a  soil  to  produce  ample  nitrate  nitrogen  to  meet 
the  requirements  of  all  growing  crops,  except  legumes,  and  to  ac- 
complish this  in  spite  of  the  natural  losses  which  are  caused  by 
rainfall,  is  a  most  important  factor  in  economical  and  maximum  food 
production, 

The  value  of  systematic  nitrate  studies  of  field  soils  is  conceded 
since  nitrogen  is  accepted  as  an  essential  plant-food  element.  It  is 
further  emphasized  by  the  fundamental  fact  that  nitrate  nitrogen  is 
the  form  of  nitrogen  utilized  by  all  non-leguminous  plants.  If  the 
supply  is  deficient  at  any  period  during  which  the  plant  requires  itr 
then  it  is  a  limiting  factor  in  crop  yields.  The  production  of  a  bushel 
of  corn  is  dependant  upon  many  factors,  any  one  of  which  .may  cause 
failure  if  operating  adversely.  Nitrates  may  be  present  in  unlim- 
ited quantities,  but  the  largest  yields  may  not  accrue  from  such  a 
condition  if  phosphorus,  or  calcium,  or  water,  or  some  other  factor, 
is  lacking.  It  is  an  important  duty  of  the  soil  biologist  to  find  meth- 
ods by  which  the  crop  demands  for  nitrate  nitrogen  will  be  amply  met 
by  the  soil  at  all  times.  This  publication  offers  information  to  that 
end. 

There  are  three  main  factors  which  exert  favorable  influences 
upon  the  production  of  nitrates  in  field  soils.  The  first  factor  is  soil 
treatment,  such  as  the  application  of  organic  matter,  limestone,  and 
phosphorus;  the  second  is  tillage  operations,  such  as  ploAving, 
cultivating,  fallowing,  and  mulching;  and  the  third,  climatic  condi- 
tions— temperature,  moisture,  and  aeration.  In  dealing  with  these  three 
factors  it  is  obviously  more  important  for  the  farmer  to  direct  his  at- 
tention to  soil  treatment,  which  he  can  control,  than  to  the  climatic 
factors,  which  can  be  only  slightly  controlled  by  farm  operations.  In- 
fluences produced  by  tillage  operations  are  under  his  control,  and 
therefore  tillage  practices  should  receive,  in  conjunction  with  soil 
treatment,  most  careful  attention.  • 


'Mr.  Schoonover,  formerly  First  Assistant  in  Soil  Biology,  was  responsible  for 
the  chemical  analyses  during  the  years  1915,  1916  and  1917,  before  enlisting  in 
lie  Sanitary  Corps  of  the  United  States  Army. 

21 


22  BULLETIN  No.  225  [March, 

There  are  a  few  definite  negative  factors  which  decrease  the 
supply  of  nitrates  in  soil.  These  are,  the  crop  grown  (including 
weeds),  rainfall,  utilization  of  nitrate  by  bacteria,  molds,  algae,  and 
other  forms  of  plant  life,  and  denitrification,  a  process  which,  how- 
ever, has  not  been  found  to  be  important  in  normal  soils.  The  crop, 
of  course,  is  not  a  factor  in  studies  of  fallow  soils. 

Of  all  the  positive  factors,  the  organic  matter  in  the  form  of 
green  manures,  farm  manures,  and  crop  residues  is  the  most  impor- 
tant, and  attention  to  it  will  produce  the  greatest  increase  in  nitrate 
production  because  it  .is  the  source  of  nitrogen  from  which  the  nitrate 
is  manufactured.  Other  kinds  of  soil  treatment,  such  as  the  appli- 
cation of  limestone  or  of  rock  phosphate,  exert  a  very  great  in- 
fluence on  nitrate  production  when  a  base  is  lacking  to  neutralize 
acid  and  when  calcium  is  needed  as  a  food,  or  when  phosphorus 
is  deficient  either  for  the  plant  or  for  the  bacteria.  These  two 
positive  factors  are  both  easily  controlled  and  are  direct  in  their 
action.  While  it  is  true  that  temperature  controls  the  course  of 
nitrate  production,  the  total  amount  and  rate  at  which  it  is  produced, 
which  are  the  vital  considerations,  are  functions  of  the  organic  matter, 
of  limestone  and  phosphorus,  and  of  tillage  operations. 

It  is  well  known  that  all  plants  and  animals,  people  included, 
require  more  food  at  certain  periods  in  their  development  than  at 
others.  Inasmuch  as  all  crops  except  legumes  obtain  their  nitrogen 
in  the  form  of  nitrate,1  from  the  soil,  it  will  not  be  out  of  place  to 
expand  the  first  statement  of  the  introduction:  At  those  stages 
when  the  crop  demands  a  large  amount  of  nitrate,  there  should  be  a 
large  reserve  in  the  soil,  or  at  least  the  soil  should  possess  the  ability 
to  meet  the  crop  requirements,  however  large  they  may  be.  If  this 
is  accomplished,  then  nitrogen  ceases  to  limit  crop  production.  If 
a  large  nitrate  reserve  is  built  up  ahead  of  consumption  by  the  crop, 
the  critical  period  is  likely  to  be  passed  without  the  slowing  down 
of  crop  growth  or  the  delaying  of  maturity.  Further,  with  a 
large  reserve  the  later  demands  made  upon  the  soil  by  the  growing 
crop  are  much  more  easily  met  by  a  normal  rate  of  nitrate  pro- 
duction. 

A  knowledge  of  the  amount  of  nitrate  present  in  Illinois  soils  un- 
der various  kinds  of  soil  treatment  is  especially  desirable  at  this  time. 


*No  evidence  has  been  found  to  support  the  view  that  ammouia  is  directly 
assimilated  by  farm  crops  in  these  soils.  Ammonia  determinations  were  made 
on  many  samples  of  these  soils  which  afforded  excellent  comparisons  with  the 
nitrates.  However,  the  results  have  no  practical  significance.  The  results  were 
consistently  around  5  to  12  pounds  per  acre  except  where  large  applications  of 
stable  manure  had  been  made.  Aeration  with  magnesium  oxid  was  used  to  de- 
termine the  ammonia. 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  23 

The  acute  situation  in  which  many  eastern  and  southern  farmers 
find  themselves  on  account  of  the  high  cost  of  commercial  nitrogen 
and  the  failure  to  take  advantage  of  the  nitrate  production  which 
is  possible  on  the  farm,  suggests  the  significance  of  such  a  study  of 
Illinois  soils. 

Chili  saltpeter,  or  sodium  nitrate,  the  cheapest  source  of  com- 
mercial nitrogen  available  in  large  amounts,  had  reached  a  figure  be- 
fore the  war  which  brought  the  cost  of  nitrogen  to  18  to  20  cents  per 
pound.  In  1918  the  federal  government  controlled  the  supply  of  so- 
dium nitrate  in  this  country  and  sold  it  to  the  farmers  at  $75.50  per 
ton,  cash  at  the  seaboard.  Nitrogen  in  this  form  cost  in  Illinois  approx- 
imately 27  cents  per  pound  at  the  railroad  station.  As  a  food 
emergency  measure  one  would  not  question  using  this  nitrogen,  even 
at  a  higher  cost,  on  the  poorer  lands  of  the  eastern  and  southern 
states;  but  continued  reliance  upon  it  under  peace  conditions,  for 
growing  staple  crops,  is  indicative  of  faulty  soil  science  and  of  a 
failure  to  utilize  our  unlimited  natural  farm  resources. 

PURPOSE  OF  INVESTIGATION 

The  investigations  reported  herein  were  undertaken  in  order 
to  systematically  measure  the  amount  and  rate  of  nitrate  production 
in  certain  surface  soils  of  Illinois,  principally  with  respect  to  the 
influence  exerted  by  seasonal  changes,  soil  treatment,  different  crops, 
and  rainfall. 

Answers  to  the  following  questions  have  been  gained  by  the 
data  obtained : 

1.  What  influence  may  proper  soil  treatment  exert  on   the 
amount  and  rate  of  nitrate  production  in  Illinois  soils  ? 

2.  Will  the  nitrogen  of  a  green-manure  crop  plowed  under  in 
the  spring  be  available  to  the  succeeding  crop  of  that  year,  and  how 
does  it  compare  with  stable  manure  in  the  rate  at  which  it  will 
produce  nitrate  for  the  succeeding  crop  ? 

3.  How  do  different  cropping  systems  affect  the  amount  of 
nitrate  produced? 

4.  At  what  time  of  year  does  the  maximum  production  of 
nitrates  occur? 

5.  What  are  the  relative  rates  of  nitrate  production  during 
the  four  seasons  of  the  year?  « 

6.  Which  of  the  farm  practices  observed  tends  to  decrease  the 
loss  of  nitrate  which  occurs  as  a  result  of  leaching? 

7.  What  are  the  periods  of  greatest  nitrogen  utilization  by  the 
corn  crop  ? 


24  BULLETIN  No.  225  [March, 

EFFECT  OF  SOIL  TREATMENT  ON  AMOUNT  OF  NITRATE  PRODUCED 

Soil  treatment  exerts  the  greatest  influence  upon  the  amount  of 
nitrate  produced. 

In  an  earlier  paragraph  the  importance  of  organic  matter  was 
mentioned.  It  can  hardly  be  emphasized  enough,  as  will  be  seen  by 
a  study  of  the  data  herein  presented,  for  the  largest  increase  in 
nitrate  production  is  derived  from  applications  of  organic  matter. 

Limestone  causes  increases  in  nitrates  even  on  poor  soils,  but  it 
is  easily  seen  that  continued  liming,  without  applications  of  organic 
matter,  would  lead  to  crop  failure  because  of  a  deficiency  of  nitrogen 
out  of  which  to  make  nitrate.  The  application  of  limestone  for 
legumes  and  the  plowing  under  of  legumes  bring  about  both  direct 
and  indirect  increases  in  nitrates. 

It  has  been  shown  in  earlier  work  at  this  station  that  tricalcium 
phosphate  furnishes  the  base  calcium  for  nitrate  formation  and,  at 
the  same  time,  phosphorus  is  made  soluble.1  Crop  residues,  stable 
manures,  and  green  manures,  with  natural  phosphates,  added  to  the 
soil,  effect  not  only  the  liberation  of  the  phosphorus  and  potassium 
from  the  soil,  thereby  meeting  the  requirements  of  large  crop  yields, 
but  they  also  produce  an  increased  accumulation  of  nitrates. 

In  the  proper  use  of  these  three  substances — organic  matter, 
limestone,  and  phosphorus — lies  the  way  of  solving  the  problem  of 
sufficient  nitrate  production  for  all  crops.  If  these  are  given  intel- 
ligent attention,  along  with  tillage  operations,  then  the  farmer  will 
have  left  nothing  undone  on  his  part  to  insure  a  sufficient  nitrate 
supply. 

INFLUENCE  OF  TILLAGE  ON  NITRATE  PRODUCTION 

Experiments  on  the  influence  of  plowing,  cultivating,  mulching, 
and  fallowing,  in  their  direct  and  indirect  effect  upon  nitrate  pro- 
duction, have  been  reported  from  Rothamsted  in  England,  from 
Samara  in  Russia,  and  from  the  Wisconsin,  Kansas,  New  York 
(Cornell),  and  Illinois  agricultural  experiment  stations.  Certain 
facts  are  outstanding  in  these  results  and  a  brief  consideration  of 
them  is  pertinent: 

Plowing  increases  nitrate  production.  Cultivation  conserves 
nitrates  by  preventing  weeds  from  using  part  of  the  available  supply. 
Mulching  reduces  loss  by  rapid  leaching  and  conserves  moisture, 
thereby  tending  to  maintain  the  nitrate  supply  in  the  soil.  Fallow- 
ing enables  the  soil  to  accumulate  large  amounts  of  nitrates  because 
none  are  removed  by  a  growing  crop. 

1See  Bui.  190,  Soil  Bacteria  and  Phosphates,  111.  Agr.  Exp.  Sta.  1916. 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  25 

Plowing  is  an  essential  farm  operation  for  the  production  of 
most  crops.  Even  tho  it  had  no  beneficial  influence  in  connection 
with  the  maintaining  of  fertility,  it  would  have  to  be  carried  out  for 
other  purposes,  such  as  the  preparation  of  the  seed  bed.  Its  relation 
to  nitrate  production  is  this:  In  plowing,  the  whole  zone  in  which 
the  nitrates  are  produced  is  mixed  and  aerated,  and  a  large  amount  of 
nitrate-producing  material  is  thereby  often  incorporated  in  the  well- 
aerated  soil.  The  whole  nitrate-producing  zone  is  in  no  way  sealed 
up.  Early  plowing  compared  with  late,  and  spring  plowing  compared 
with  fall,  as  influencing  nitrate  production  under  satisfactory  experi- 
mental conditions,  have  not  been  studied  for  humid  regions.  Kesults 
from  five  years'  determinations  at  Samara,  Russia,  altho  obtained  in 
the  semiarid  region,  demonstrated  the  value  of  fall  and  early  spring 
plowing  over  later  plowing,  as  in  May  and  June.  In  Kansas,  plowing 
in  July  was  superior  to  August,  August  was  superior  to  September, 
and  September  was  superior  to  October,  for  winter  wheat. 

Unless  a  green  manure  is  to  be  plowed  under  just  before  seeding 
wheat,  the  land  should  be  plowed  early  in  the  summer  after  the  removal 
of  the  crop.  In  following  this  method,  moisture  and  nitrates  are  con- 
served and  nitrate  production  encouraged.  In  some  seasons  these 
effects  may  be  considerable.  Where  a  crop  of  green  clover  is  plowed 
under,  rapid  decomposition  results  and  early  plowing  is  not  so  essen- 
tial from  the  standpoint  of  nitrate  production. 

The  data  regarding  cultivation  as  a  means  of  increasing  nitrates 
are  very  conflicting.  If,  however,  cultivation  is  considered  to  be  for 
the  purpose  of  killing  weeds,  then  it  is  not  necessary  to  emphasize 
its  value  as  a  means  of  conserving  nitrates  for  the  crop.  If  weeds 
are  not  a  consideration,  then  the  problem  becomes  different.  The 
effect  produced  by  cultivation  is  undoubtedly  related  to  soil  conditions. 
The  late  Professor  King  expressed  the  belief  that  the  cultivation  of 
a  wet  soil  was  detrimental  because  of  the  sealing  up  of  the  nitrate- 
producing  areas.  It  must  be  understood,  however,  that  cultivation  is 
not  to  be  compared  with  plowing,  for  cultivation  stirs  only  the  surface 
soil  and  seldom  disturbs  the  most  important  nitrate-producing  zone. 
The  opinion  is  even  held  by  some  that  cultivation  does  not  add  air  to 
a  soil.  If  cultivation  is  to  be  practiced  for  any  purposes,  including 
the  killing  of  weeds,  it  should  certainly  be  shallow  in  order  not  to 
injure  the  crop. 

THE  COURSE  OF  NITRATE  PRODUCTION  IN  FIELD  SOILS  -  * 

That  climatic  factors  influence  nitrate  production  in  soils  has 
already  been  stated.  The  results  obtained  in  various  parts  of  the 
world  are  in  agreement  as  to  the  effect  exerted  by  increasing  temper- 
atures in  spring  and  early  summer.  Since  the  production  of  nitrates 
is  the  result  of  a  series  of  biochemical  reactions,  production  is  increased 


26  BULLETIN  No.  225  [March, 

in  a  manner  similar  to  most  chemical  reactions — by  a  rise  in  temper- 
ature. The  actual  course  of  nitrate  production  in  Illinois  is  as  follows : 

During  the  winter  no  nitrate  is  produced,  because  of  low  tem- 
peratures, and  none  is  lost  while  the  soil  is  frozen ;  b'ut  as  soon  as  the 
soil  thaws,  if  heavy  rains  occur,  a  loss  of  nitrate  results.  With  the 
rising  temperature  .of  early  spring  the  ammonifying  and  nitrifying 
organisms  multiply,  and  a  gradual  increase  in  nitrate  production  sets 
in  usually  in  March  or  early  April.  Cold,  wet  periods  often  retard 
nitrate  production  at  this  time  of  the  year,  and  rains  are  rather  dis- 
astrous if  many  occur  in  a  short  period.  In  the  month  of  May,  when 
there  is  usually  a  marked  rise  in  temperature,  nitrate  production 
increases  rapidly,  especially  during  the  latter  part  of  the  month.  In 
June  optimum  temperature  and  moisture  conditions  are  approached. 
The  greatest  rate  of  production  and  the  largest  accumulation  of 
nitrates  consequently  occur  in  this  month,  especially  is  this  true  of 
soils  plowed  in  May  or  under  preparation  for  cultivated  crops  that  are 
to  be  planted  in  May  or  June.  However,  winter  wheat,  oats,  clovers, 
alfalfa,  or  other  crops  on  the  land  in  March  or  April  may  so  affect  con- 
ditions that  the  largest  accumulation  does  not  appear  in  June,  but  in 
May.  These  crops  protect  the  soil  from  excessive  losses  and  use  the 
largest  amount  of  nitrate  in  late  May  and  early  June.  Immediately 
after  their  removal  nitrate  production  falls  to  a  low  ebb,  usually  owing 
to  excessive  dryness. 

In  a  wet  summer,  nitrates  are  produced  in  relatively  large  amounts 
during  July  and  August,  but  usually  with  the  coming  of  midsummer, 
the  combination  of  temperature  and  moisture  conditions  is  such  as  to 
cause  a  very  great  reduction  of  nitrate  production  in  most  soils  in  this 
climate.  Land  in  corn  shows  a  marked  decrease  in  nitrates  after  the 
crop  is  laid  by  and  no  tendency  in  normal  summers  to  recover  the 
same  efficiency  which  it  displays  in  June.  Even  in  the  case  of  land  on 
which  wheat  and  oats  have  been  cut,  little  nitrate  production  occurs 
when  the  two  months  of  July  and  August  are  considered  as  a  whole. 
Showers  at  this  time  often  cause  an  increase,  but  no  continuous  ten- 
dency toward  large  production  has  been  observed.  In  fallow  soils 
nitrate  formation  increases  during  these  months,  but  at  a  slower  rate 
than  during  May  and  June. 

A  second  rise  in  nitrate  production  always  occurs  in  September, 
October,  and  sometimes  November.  Temperature  and  moisture 
conditions  seem  to  approach  a  second  optimum  in  those  months,  altho 
the  increase  in  late  summer  and  fall  is  not  usually  so  great  as  in  late 
spring  and  early  summer.  Production  ceases  with  the  approach  of 
winter. 

The  course  of  nitrate  production  is  not  widely  different  for  nor- 
mal seasons,  but  it  does  change  with  moist  summers,  when  nitrates  are 
likely  to  be  produced  in  larger  amounts  than  in  a  normal  summer, 


1920]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  27 

and  with  open,  mild  winters,  when  the  losses  are  greater  than  in 
winters  of  normal  temperature. 

INTERPRETATION  OF  EXPERIMENTAL  EESULTS 

In  presenting  the  results  which  follow  it  has  been  found  advisable 
to  report  the  actual  pounds  per  acre  of  nitrogen  as  nitrate,  at  the 
various  dates  of  sampling.  Each  figure  is  an  average  of  two  deter- 
minations, each  determination  being  that  of  a  field  sample  consisting  of 
twelve  to  fifteen  cores,  according  to  the  crop  and  plot.  The  plots  on 
the  North  Farm  are  one-tenth  acre  each  and  those  on  the  South 
Farm,  one-fifth  acre  each. 

The  method  of  presenting  the  results  permits  a  study  of  the  extent 
of  the  fluctuations,  and  when  the  rainfall  is  noted,  together  with  the 
kind  of  crop  grown,  the  causes  of  such  fluctuations  are  apparent. 
This  is  important,  for  the  belief  has  been  expressed  that  nitrates  were 
extremely  liable  to  fluctuations  which  rendered  their  determination  of 
no  value.  The  fact  is  the  exact  opposite.  Definite  causes  for  all  the 
fluctuations  are  very  accurately  and  easily  found  if  the  fluctuations 
are  only  studied  thoroly.  It  is  perfectly  evident  that  if  only  sporadic 
attempts  at  determining  nitrates  are  made,  unreliable  conclusions  will 
result. 

In  examining  the  results  one  must  not  overlook  the  influence  of 
the  crop.  As  an  illustration,  Plots  501  and  510  of  the  Davenport 
series  may  be  used.  Plot  501  is  a  poor  producer  of  nitrate  compared 
with  Plot  510.  If  however,  some  element  other  than  nitrogen  is  lim- 
iting crop  growth  on  Plot  501,  then  even  when  corn,  for  example,  is 
at  the  period  of  greatest  growth,  a  large  surplus  of  nitrate  may  be 
found.  On  the  same  date  Plot  510,  supporting  a  larger  growth,  may 
show  less  nitrate  than  Plot  501.  But  the  fact  that  Plot  510  is  a  better 
nitrate-producing  plot  will  be  shown  by  its  record  of  two  or  three 
weeks  before  or  a  week  or  more  later.  It  may  even  happen  that  the 
best  plot  will  show  consistently  less  accumulation  than  some  other 
plots,  and  in  such  case  the  crop  yield,  or  still  better,  a  determination 
made  without  the  presence  of  a  crop,  will  assist  in  indicating  the  true 
condition.  It  is  difficult,  however,  in  some  cases  to  measure  all  the 
nitrate  produced,  for  the  reason  that  a  catch  crop  grown  for  green 
manure  will  reduce  the  nitrate  temporarily,  altho  it  will  greatly  in- 
crease it  when  later  plowed  under.  In  the  course  of  a  rotation  these 
effects  are  all  considered  and  their  true  results  measured.  * 

Limestone  increases  nitrate  production  but  it  also  greatly  benefits 
legumes,  which  may  take  up  the  extra  nitrate  produced  at  certain 
times ;  and  it  therefore  becomes  difficult  always  to  determine  immedi- 
ately the  exact  effect  of  one  factor  in  a  series  of  combinations.  When 
no  crop  occupies  the  land,  a  comparison  of  the  effects  of  given  treat- 
ments is  much  easier  to  obtain. 


28  BULLETIN  No.  225  [March, 

The  presence  of  nitrate  in  soil  growing  a  crop,  combined  with  a 
study  of  various  treatments,  nevertheless  serves  to  answer  the  question 
whether  the  soil  is  ahead  of  the  nitrate  needs  of  the  /»rop.  A  method 
of  ascertaining  the  nitrate-producing  ability  of  the  soil  when  an 
analysis  of  the  field  samples  shows  no  surplus  will  be  described  later. 

All  the  results  included  in  this  bulletin  are  expressed  in  pounds 
of  the  element  nitrogen  in  the  form  of  nitrate,  per  acre  of  surface  soil 
(the  soil  from  about  0  to  6%  inches  in. depth).  Fourteen  pounds  of 
nitrogen  are  equivalent  to  62  pounds  of  nitrate  radicle  (NO3),  or  85 
pounds  when  reported  as  pure  sodium  nitrate  (NaN03)  or  pure 
"  Chilisaltpeter. "  The  figures  reported  are  averages  of  duplicate  field 
samples  in  all  cases,  unless  otherwise  indicated,  and  in  some  cases  they 
represent  averages  of  four,  eight,  and  sixteen  determinations. 

The  column  headed  "Apparent  utilization  of  nitrogen,"  must 
be  understood  to  represent  the  minimum  utilization  of  nitrogen,  for 
no  method  was  used  by  which  it  could  be  exactly  determined  how  much 
nitrate  may  have  been  produced  and  used  during  each  period.  It  is 
possible  to  show  therefore,  as  nitrate  utilization,  only  the  amount  of 
decrease  between  an  earlier  and  a  later  date.  A  more  exact 
figure  could  be  obtained  by  making  analysis  of  the  crops,  but 
that  was  not  possible  in  these  long-continued  experiments.  How- 
ever, as  these  figures  are  comparative  they  do  not  represent  as  great 
fluctuations  from  the  actual  as  might  at  first  appear,  especially  is  this 
true  of  determinations  made  during  a  normal  season  and  about  the 
critical  period  for  corn  (June  25  to  July  15)  because,  owing  to  de- 
creased rainfall  and  increased  temperature,  there  is  a  rapid  falling 
off  in  nitrate  production  at  that  time.  It  is  evident  that  where  pro- 
duction had  ceased  the  figures  would  approach  a  high  degree  of  ac- 
curacy. 

Moisture  determinations  are  included  in  all  cases,  as  they  are 
important  in  nitrate  studies  and,  further,  have  a  value  in  showing  the 
relation  between  climatic  conditions  and  the  actual  moisture  content 
of  these  field  soils.  The  figures  given  show  the  number  of  tons  of 
water  accompanying  two  million  pounds  of  water-free  soil.  Certain 
facts  connected  with  these  determinations  will  be  indicated  elsewhere. 


1980]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  29 


NITRATE  PRODUCTION  IN  CORN-BELT  SOILS 


The  first  studies  included  in  this  report  were  conducted  in  1915 
on  certain  plots  of  the  Davenport  series  on  the  North  Farm,  at  Urbana.1 

On  these  five  series  a  rotation  is  practiced  consisting  of  wheat, 
corn,  oats,  and  clover,  with  a  fifth  field  in  alfalfa  for  five  years,  after 
which  it  is  rotated  with  the  other  four  crops  while  the  alfalfa  is  grown 
on  another  of  the  series  for  five  years.  This  rotation  has  been  prac- 
ticed since  1911,  and  the  reader  is  referred  to  Illinois  soil  reports  for 
earlier  and  more  detailed  information  regarding  these  series.  A  few 
brief  statements  are  necessary  here  to  explain  the  soil  treatment  on 
the  plots  listed  below,  which  were  selected  for  study.  In  the  beginning 
the  six,  plots  selected  were : 

1  No  treatment  (except  a  rotation  of  crops) 

2  Residues 

3  Manure 

4  Eesidues,  limestone 

6     Eesidues,  limestone,  phosphorus 
10     Manure,  limestone,  phosphorus 

On  the  residues  plots  the  corn  stalks  are  left  standing  and  the 
wheat  and  oat  straws  returned,  as  are  also  clover  hullings  and,  in  the 
main,  all  legumes  except  alfalfa  and  the  legume  seeds.  Catch  crops 
of  sweet  clover  or  mixtures  of  clovers  are  seeded  in- the  wheat  on  the 
residues  plots  and  on  the  plots  receiving  extra  heavy  treatment  (No. 
10  of  each  series),  and  are  plowed  under  in  the  following  spring  for 
corn.  A  catch  crop  has  been  seeded  in  the  corn  but  has  not  been  suc- 
cessful. The  manure  plots  receive  applications  of  farm  manure  in 
amounts  corresponding  to  what  could  be  made  from  the  crops  pro- 
duced, and  all  residues  and  grains  are  removed.  The  manure  is  ap- 
plied in  the  fall  or  winter,  for  the  corn  crop,  and  is  plowed  under. 

Limestone  is  applied  at  the  rate  of  two  tons  per  acre  every  four 
years  and  at  the  rate  of  two  and  one-half  tons  per  acre  for  the  alfalfa 
once  in  five  years.  The  application  is  made  ahead  of  the  wheat  and  is 
disked  in. 

Bone  meal  has  been  applied  on  the  east  half  of  each  series,  at  the 
rate  of  800  pounds  per  acre,  once  in  four  years ;  and  raw  rock  phosphate, 
has  been  applied  on  the  west  half  at  the  rate  of  2,400  pounds  per  acre, 
once  in  four  years.  The  phosphate  is  applied  ahead  of  the  corn,  it 
being  plowed  under  with  the  manure  and  residues.  No  attempt  was 
made  to  study  the  influence  of  each  form  of  phosphorus  on  nitrate 
production. 


JSee  appendix  for  method  of  determining  nitrates,  used  in  these  investigations. 


30  BULLETIN  No.  225  [March, 

NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1915 
SERIES  400,  UNIVERSITY  NORTH  FARM 

Series  400  on  the  North  Farm  at  Urbana  was 'the  first  series 
studied.  This  series  had  grown'  wheat  in  1914,  and  the  wheat  straw, 
manure,  and  phosphates  were  applied  and  plowed  under  in  the  fall. 

Corn  was  planted  in  1915  in  the  usual  manner.  The  first  samples 
for  nitrate  determination  were  taken  on  June  17.  The  corn  was  laid 
by  about  July  1. 

Table  1  shows  the  amounts  of  nitrate  nitrogen  found  on  the  dates 
of  sampling.  The  apparent  amount  disappearing  between  June  28  and 
July  15,  or  17  days  during  the  rapid  growth  of  crop,  is  shown  in  the 
sixth  column.  It  should  be  stated  that  the  rainfall  was  high  during 
this  season,  5.17  inches  occurring  in  28  days  and  3.85  inches  during 
the  seventeen-day  period  chosen.1  The  distribution  of  the  rainfall  was 
such  that  it  appeared  not  to  reduce  the  supply  of  nitrate,  and  the  re- 
duction found  is  therefore  assigned  to  that  taken  up  by  the  corn  crop. 
Observations  on  the  growth  of  the  corn  were  in  accordance  with  the 
rapid  use  of  nitrate  recorded. 

The  yields  of  corn  are  given  in  the  last  column  for  comparison 
with  the  amount  of  nitrate  nitrogen  used  during  this  seventeen-day 
period.  While  there  is  a  direct  relationship  between  the  amount  of 
nitrate  present  and  crop  yielcj,  it  does  not  always  appear,  for,  as 
earlier  stated,  other  factors  may  be  operating  to  limit  crop  produc- 
tion when  nitrates  are  plentiful. 

The  two  manure  plots  were  apparently  using  the  nitrate  earlier 
than  the  others:  Plot  403,  receiving  manure  alone,  shows  a  decrease 
of  10  pounds  from  June  17  to  June  28,  which  added  to  the  apparent 
utilization  from  June  28  to  July  15  makes  a  total  of  26.5  pounds,  or 
the  same  amount  as  determined  for  the  plot  receiving  residues,  lime- 
stone, and  phosphorus,  (No.  406),  with  identical  crop  yields.  The 
manure  is  known  to  decompose  faster  than  the  straws  of  small  grains. 
It  sometimes  contains  urea,  which  is  rapidly  converted  into  nitrate 
under  favorable  conditions;  and  certain  other  compounds  in  manure 
are  transformed  faster  than  the  nitrogen  of  straws.  The  manure 
shows  its  true  relationship  here,  as  both  manure  and  residues  were 
applied  at  the  same  time. 

Plot  410,  receiving  the  extra-heavy  manure  treatment  (where 
manure  is  applied  in  quantity  five  times  the  usual  amount),  along 
with  phosphorus  and  limestone,  did  not  show  five  times  as  much  nitrate 
on  June  17  as  that  found  on  the  plot  receiving  manure  alone  (No.  403), 
but  only  1.26  times  as  much ;  but  on  June  28  it  still  contained  about 
20  pounds  more  than  Plot  403.  The  nitrogen  appears  to  be  in  great 

irrhe  rainfall  data  reported  in  this  bulletin  were  obtained  from  records  of 
the  soil  physics  division  of  the  Agronomy  Department. 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


31 


TABLE  1. — NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1915:  SERIES  400, 
UNIVERSITY  NORTH  FARM 

Pounds  per  acre  in  2  million,  pounds  of  surface  soil   (about  0  to  6J3  inches), 
water-free  basis 


Plot 

Treatment 

Date  of  sampling 

Apparent 
utilization 
of 
nitrogen 
in  17 
days 

Corn 
yield, 
bu. 

June 
17 

June 
28 

July 
15 

401 

402 
403 
404 
406 
410 

None  (except  crop  rota- 
tion)   

32.8 
32.2 
45.1 
32.5 
33.3 

56.8 

31.7 
32.6 
35.0 
33.9 
31.2 

54.5 

27.6 
19.7 
18.5 
12.3 
6.8 

15.4 

4.1 
12.9 
16.5 
21.6 
25.4 

39.0 

66.4 
66.8 
80.8 
73.2 
80.8 

82.0 

Residues  

Manure  

Residues,  lime  

Residues,  lime,  phosphate. 
Manure-x,    lime,    phos- 
phate-x  

TABLE  2. — MOISTURE  CONTENT  OF  THE  SOIL  GROWING  CORN  IN  1915:  SERIES  400, 

UNIVERSITY  NORTH  FARM 

Tons  of  water  with  2  million  pounds  of  surface  soil  (about  0  to  &2/z  inches), 
water-free  basis1 


Pint 

I 

)ate  of  sampling 

p 

Treatment 

June  17 

June  28 

July  15 

401 

None  

244.6 

241.5 

251.5 

402 

R  

243  0 

266.1 

248.4 

403 

M  

237  3 

237.6 

240.7 

404 

RL  

240.7 

232.3 

251.6 

406 

RLP  

246.1 

239.9 

255.7 

410 

MxLPx  

241  .4 

246.9 

264.4 

JIt  is  a  simple  matter  to  change  tons  of  water  per  acre  to  equivalent  inches  of 
rainfall  by  dividing  the  tons  per  acre  by  113.25,  which  is  the  weight  in  tons  of 
an  acre-inch  of  water.  By  moving  the  decimal  point  in  any  of  the  figures  in 
these  moisture  tables  one  place  to  the  left,  the  percentage  of  water,  as  expressed 
on  an  arbitrary  water-free  basis,  is  obtained.  The  percentage  of  moisture  on  the 
field  basis  is  obtained  by  adding  1000  to  any  figure,  dividing  the  original  figure 
by  that  sum,  and  then  pointing  off  two  places. 

excess  on  this  plot,  and  was  not  used  economically  for  grain  produc- 
tion. 

These  results  do  not  indicate  that  nitrate  nitrogen  was  limiting 
crop  production,  at  least  as  late  as  July  15,  with  crops  of  this  magni- 
tude, for  the  check  plot  on  that  date  still  contained  27.6  pounds,  having 
used  apparently  only  4.1  pounds  in  the  seventeen-day  period,  and  Plot 
410,  which  had  apparently  used  about  ten  times  the  amount  used  on 
the  check  plot,  still  contained  15.4  pounds.  The  corn  on  Plot  410  grew 
much  faster  than  on  the  check,  but  not  six  times  as  fast.  The  highest 
yielding  plots  produced  more  stalks,  and  these  are  undoubtedly  richer 
in  nitrogen,  which  condition  disturbs  the  normal  ratio  between  nitro- 
gen assimilated  and  yield  of  grain.  The  residues-limestone-phos- 
phorus plot  (No.  406),  with  the  lowest  nitrate-nitrogen  content  on 
June  28,  appears  to  have  had  the  better  balance  of  plant-food  elements, 
and  here  the  nitrate  nitrogen  was  more  economically  used. 


32  BULLETIN  No.  225  .  [March, 

It  is  difficult  to  conceive  how  an  application  of  a  nitrogenous  fer- 
tilizer, even  if  it  contained  nitrate  nitrogen,  could  have  been  of  any 
value  on  these  plots  when  the  corn  was  laid  by,  for  the  lowest  nitrate 
content  still  unused  in  the  surface  soil  of  any  plot  was  the  equivalent 
of  40.8  pounds  of  sodium  nitrate,  or  200  pounds  of  3.4-percent  nitrog- 
enous fertilizer. 

NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1916 
SERIES  500,  UNIVERSITY  NORTH  FARM 

Alfalfa  was  seeded  on  this  series  in  1911  but  failed  and  was  re- 
seeded  in  1912.  Hay  crops  were  removed  from  all  plots  during  1912, 
1913,  1914,  and  1915.  The  stubble  was  plowed  under  in  March,  1916, 
together  with  manure  and  phosphate,  and  the  limestone  applied  in 
May. 

The  results  of  determinations  for  nitrate  nitrogen  are  found  in 
Table  3.  The  high  content  of  nitrate  nitrogen  is  important  to  ob- 
serve: the  alfalfa  stubble  appears  to  be  easily  decomposed  and  must 
be  rich  in  nitrogen.  The  presence  of  a  crop  of  this  kind  on  the  land 
also  assists  in  preventing  losses  from  leaching  by  taking  up  large 
amounts  of  available  nitrogen  and  by  preventing  the  rapid  downward 
flow  of  water.  Even  on  the  plot  receiving  no  treatment  the  produc- 
tion of  nitrate  nitrogen  is  shown  to  have  been  high  and  it  was  probably 
much  higher  on  all  plots  than  it  would  have  been  if  hot  dry  winds  had 
not  injured  the  pollen  at  the  time  of  fertilization  and  by  reducing 
crop  yields  reduced  the  utilization  of  nitrate  nitrogen. 

There  is  an  increase  shown  on  all  plots,  from  April  4  to  June  5, 
except  on  Plot  510.  The  decrease  on  Plot  510  between  May  11  and 
June  5  is  related  to  the  rapid  growth  of  the  crop,  which  is  always 
evident  here  and  which  is  also  evident  at  times  on  Plot  6  of  each  series 
at  a  much  earlier  period  than  on  the  other  plots.  A  decrease  is  noted 
on  all  plots  from  June  5  to  June  26. 

The  high  moisture  content  from  June  5  to  June  26,  with  3.44 
inches  of  rainfall  well  distributed  over  the  period,  so  slowed  down 
nitrate  production  that  consumption  by  the  plant  became  greater  than 
production,  and  a  consequent  reduction  in  nitrate  is  seen  to  have  taken 
place.  The  increase  which  followed  in  the  next  period  was  due  to  the 
reduced  moisture  content  furnishing  more  favorable  conditions  as 
regards  oxygen  supply. 

The  temperature  from  August  11  to  August  23  was  an  important 
factor  in  rapid  increase,  as  it  appears  to  have  been  at  the  optimum, 
while  during  the  preceding  period  it  was  too  high  when  coupled  with 
the  dryness  of  the  soil. 

From  August  23  to  September  14  all  plots  except  Nos.  504  and 
510  lost  nitrates.  This  loss  is  traceable  to  a  rainfall  of  1.48  inches  on 


1920} 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


33 


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34  BULLETIN  No.  225  [March, 

September  6.  Up  to  September  14,  the  plots  had  increased  in  mois- 
ture content  75.2  tons  per  acre,  and  a  further  increase  of  89.8  tons 
appeared  by  December  6.  Under  these  conditions  one  «might  have  ex- 
pected an  increase  in  nitrate  content,  but  it  is  necessary  to  study  the 
periods  separately  in  order  to  realize  the  true  relationship  of  nitrate 
production  to  rainfall. 

In  the  period  from  September  14  to  October  30,  there  was  3.17 
inches  of  rainfall,  which  by  being  concentrated  greatly  reduced  the 
amount  of  nitrate  in  the  soil.  The  moisture  content  on  October  30  was 
243.4  tons,  antf.  on  November  20,  246.2  tons;  under  these  conditions 
some  plots  had  gained  nitrate.  By  reference  to  the  rainfall  records, 
one  finds  only  .78  inches  of  precipitation  in  the  twenty-one  days. 
Here  again  the  rainfall  was  not  sufficient  to  cause  a  loss  of  nitrate 
but  instead  stimulated  its  production.  A  gain  this  late  in  the  season 
is  important,  as  winter  wheat  would  often  benefit  by  the  nitrate  pro- 
duced. From  November  20  to  December  6  the  average  moisture  con- 
tent increased  from  246.2  tons  to  284.3  tons  owing  to  a  rainfall  of 
1.64  inches.  However,  as  the  rainfall  was  concentrated  a  loss  of 
nitrates  resulted. 

Attention  is  called  to  the  number  of  determinations  showing  a 
nitrate-nitrogen  content  of  more  than  35  pounds  per  acre  which  are 
recorded  for  this  series  in  this  year  even  tho  the  series  carried  the 
corn  crop.  Seventy-eight  of  the  90  figures  reported  are  above  35 
pounds  per  acre.  On  the  same  series  in  1917  (see  Table  12)  only  six 
determinations  out  of  48  were  above  35  pounds..  The  difference  in  this 
case  is  probably  related  to  the  initial  decomposition  of  the  alfalfa  roots, 
and  to  the  different  conditions  under  which  the  soil  was  placed  by  be- 
ing planted  to  crops  which  grow  at  widely  different  times.  (It  will 
be  noted  that  oats  were  grown  in  1917).  When  a  crop  is  planted  in 
May  and  does  not  begin  to  take  up  much  nitrate  until  about  the  middle 
or  last  of  June,  the  soil  is  given  ample  opportunity  to  build  up  a  large 
reserve  of  nitrate  (if  it  possesses  the  active  nitrogen),  and  it  will  meet 
the  demands  of  a  rapidly  growing  crop.  On  the  other  hand,  with  an 
early  seeded  crop  and  one  which  more  completely  covers  the  ground, 
such  as  oats,  the  accumulation  during  April,  May,  and  June  is  not  so 
great  as  where  the  land  is  fallow,  since  the  crop  is  constantly  draw- 
ing on  the  nitrate  supply  and  has  materially  reduced  it  before  the 
period  of  greatest  accumulation  is  approached. 

A  study  of  the  figures  for  Plot  510  shows  the  relative  rate  at 
which  nitrate  was  being  taken  up  by  the  corn  crop  during  certain  of 

APPARENT. NITRATE  CONSUMPTION  ON  PLOT  510,  1916 

Period  Days  Pounds 

taken  up 

June  5  to  June  26 21  11.0 

June  26  to  July  3 7  6.0 

July  3  to  July  8 5  45.7 


1920]  NITEOGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  35 

the  periods.  The  large  use  of  nitrate  on  these  plots  during  a  relatively 
few  days  is  in  agreement  with  the  results  reported  for  the  corn  crop 
of  1915  on  Series  400 ;  it  was  earlier  than  observed  in  some  of  the  other 
seasons. 

All  the  plots  in  Series  500  decreased  materially  in  nitrate- 
nitrogen  content  from  July  3  to  July  14.  On  Plots  506  and  510  the 
lowest  figures  came  before  July  8,  but  on  the  'other  plots  not  until 
July  14.  A  slight  gain  occurred  between  July  14  and  July  21.  A 
decrease  then  occurred  to  August  11,  which  indicates  that  production 
had  practically  ceased.  An  increase  is  then  noted  to  August  23. 
With  an  average  moisture  content  of  but  153.2  tons  on  July  21 
and  only  128  tons  on  August  2,  and  with  nitrates  disappearing, 
a  rainfall  of  .79  inches  on  August  11  raised  the  moisture  content  to 
178.2  tons  and  was  responsible  for  the  increase  of  the  nitrate  nitro- 
gen that  followed,  the  average  increase  for  the  series  being  20.9 
pounds  during  the  twelve-day  period.  The  moisture  content  had 
rapidly  fallen  from  July  8,  when  it  was  202.6  tons,  to  August  2,  when 
it  was  only  128  tons.  The  figures  indicate  that  a  moisture  content  of 
130  to  about  150  tons  was  not  sufficient  for  nitrate  production  at  this 
time  of  year.  An  increase  in  nitrate  was  found  when  the  moisture 
content  was  178  tons  and  even  as  the  content  decreased  to  150  tons. 

The  amounts  of  nitrate  shown  in  Table  3  as  removed  in  eleven 
days,  considered  in  connection  with  the  crop  yields,  illustrate  the  fact 
that  the  exact  relationship  between  the  amount  of  nitrate  removed 
and  crop  yields  cannot  be  ascertained  on  account  of  the  presence  of 
some  of  the  many  other  factors  which  may  influence  the  yields.  It 
must  be  admitted,  nevertheless,  that  nitrate  was  present  in  this  series 
in  large  amount,  even  after  the  crop  had  taken  up  more  than  it  needed 
to  produce  the  yields  obtained. 

Value  of  Active  Organic  Matter  in  Nitrate  Production 

If  the  results  for  the  entire  season  from  Plot  502  are  compared 
with  those  from  Plot  501,  it  will  be  found  that  Plot  502  (residues) 
produced  53.7  pounds  more  nitrate  nitrogen  than  Plot  501  (no  treat- 
ment). This  difference  is  due  to  the  effect  of  the  decomposing  crop 
residues  which  are  returned  to  the  soil,  and  to  the  larger  growth  of 
roots. 

The  manure  plot  (No.  503)  was  13.2  pounds  superior  to  the  plot 
receiving  no  treatment  (No.  501)  in  the  production  of  nitrate  nitrogen, 
when  allowance  is  made  for  the  nitrogen  difference  in  crop  yields  on 
the  basis  of  the  standard  values  for  nitrogen  in  corn ;  while  the  resi- 
dues plot  was  39.1  pounds  superior  to  the  manure  plot. 


36  BULLETIN  No.  225  [March, 

Gain  for  Phosphorus 

The  residues-limestone-phosphorus  plot  shows  ^  gain  of  8.1 
pounds  over  the  residues-limestone  plot,  as  the  average  for  the  season. 
This  plot  yielded  6.6  bushels  more  corn,  which  is  estimated  to  have 
contained  9.9  pounds  of  nitrogen.  Figured  in  this  manner,  we  have 
18  pounds  more  of  nitrate  nitrogen  produced  where  the  phosphorus 
was  applied. 

Gain  for  Limestone 

A  comparison  of  the  residues-limestone  plot  with  the  residues 
plot  shows  that  12.1  pounds  more  nitrate  nitrogen  was  available  in  the 
former  plot  than  in  the  latter,  while  limestone  produced  1.8  bushels 
more  corn,  which  makes  a  gain  attributable  to  limestone  of  14.8 
pounds. 

NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1917 
SERIES  200,  UNIVERSITY  NORTH  FARM 

This  series  grew  soybeans  in  1915  and  wheat  in  1916.  A  catch 
crop  of  sweet  clover  was  seeded  in  the  wheat  in  February,  1916,  on 
the  residue  plots  and  on  Plot  210.  The  sweet  clover  made  an  excel- 
lent growth  in  the  spring  of  1917.  In  March  the  manure  and  phos- 
phates were  applied.  The  land  was  plowed  on  May  3  and  the  corn 
planted  May  14. 

In  Table  5  are  given  the  results  obtained.  It  will  be  noted  that 
an  increase  in  nitrate  production  occurred  on  four  plots  up  to  July  7, 
when  the  usual  tendency  to  decrease  was  manifest,  and  as  noted  in 
1915  and  1916  the  richest  plot  in  this  series  (No.  210)  showed  the 
decrease  at  the  earliest  date.  Spring  rains  were  not  very  disastrous. 
There  was  only  5.73  inches  of  rain  from  March  15  to  May  19.  Losses 
of  nitrate  are  apparent  on  Plot  201,  which  had  no  green-manure  crop, 
and  on  Plot  202,  which  had  but  little  protection  as  the  green-manure 
crop  was  very  poor.  The  heavy  rainfall  in  the  period  from  May  19  to 
June  18  was  so  scattered  and  the  moisture  content  of  the  soil  was 
such  that  only  slight  losses  were  evident.  During  the  remainder  of 
the  season  the  rain  was  not  sufficient  to  cause  a  loss  until  in  October, 
when  a  decrease  is  seen. 

Very  interesting  differences  in  the  color  and  the  height  of  the 
corn  on  the  residues  plots  as  compared  with  the  manure  plots  de- 
veloped early  in  July  thruout  the  series.  Results  bearing  on  the  value 
of  sweet  clover,  which  was  the  cause  of  the  differences  observed,  for 
nitrate  production,  are  reported  for  the  1918  corn  crop.  Attention 
should  be  directed  to  the  much  slower  growth  of  the  corn  this  year 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


37 


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38  BULLETIN  No.  225  [March, 

compared  with  that  of  similar  periods  in  previous  years,  as  evidenced 
by  the  small  amounts  of  nitrate  removed  in  the  twelve-day  period  at 
about  the  time  the  corn  was  laid  by. 

NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1918 
SERIES  300,  UNIVERSITY  NORTH  FARM 

This  series  was  in  wheat  in  1917 ;  sweet  clover  was  seeded  on  the 
residues  plots  and  also  on  Plot  310.  The  manure  was  applied  during 
the  winter,  and  both  it  and  the  sweet  clover  were  plowed  under  at  the 
same  time.  The  growth  of  sweet  clover  was  excellent.  All  ten  plots 
were  studied  this  year.  As  it  had  been  found  that  samples  taken  a  few 
weeks  before,  during,  and  a  little  after  the  critical  periods  of  crop 
growth  were  a  sufficient  basis  upon  which  to  judge  the  nitrate  pres- 
ent and  the  rate  of  accumulation  for  the  crop,  fewer  samples  were 
taken  on  this  series  than  on  the  others. 

In  Table  7  are  presented  important  results  showing  the  effect 
of  sweet  clover  when  plowed  under  green,  upon  nitrate  production, 
and  the  differences  between  its  effect  and  that  of  the  stable  manure 
which  was  applied  to  some  of  the  plots  of  the  series.  Very  notice- 
able differences  in  the  color  and  height  of  the  corn  appeared  in  favor 
of  the  residues  plots.  (The  sweet  clover  is  grown  in  addition  to  the 
regular  crop  residues,  and  when  plowed  under  young  may  contain 
100  pounds  of  nitrogen  per  ton  of  dry  matter,  and  probably  even  con- 
tains some  nitrate  at  that  stage.) 

A  comparison  of  the  figures  for  the  residues  plots  and  those  for 
the  manure  plots  demonstrates  in  a  concise  manner  the  superiority, 
this  season,  of  the  sweet  clover  over  the  manure  for  nitrate  produc- 
tion. While  there  appears  to  be  some  tendency  for  the  manure  to 
reduce  the  differences  later  in  the  season,  the  reduction  is  not  large. 
In  75  percent  of  the  determinations  the  sweet  clover  proved  to  be 
superior  to  the  manure,  and  where  inferior,  it  was,  except  in  one 
case,  either  during  rapid  growth  of  the  crops  or  later,  which  surely 
detracts  little  from  the  value  of  the  sweet-clover  results.  Only  once 
did  the  normal  manure  plots  reach  40  pounds,  while  the  sweet-clover 
plots  exceeded  even  this  figure  in  twelve  cases  out  of  twenty-four.  The 
ordinary  run  of  manure,  by  the  time  it  is  applied  to  the  soil,  has  lost 
a  large  part  of  its  rapidly  decomposing  nitrogenous  compounds,  and 
the  nitrate  production  resulting  from  its  application  should  be  ex- 
pected to  be  less  rapid  than  that  from  a  green  manure.  The  increase 
found  here,  on  a  relatively  good  soil,  from  sweet  clover,  suggests  what 
may  be  possible  in  the  way  of  insuring  the  success  of  this  legume  thru 
applications  of  limestone  and  phosphorus.  The  plots  which  had  made 
the  largest  growth  of  sweet  clover  were  the  plots  receiving  the  best 


1930} 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


39 


TABLE  7.  —  NITRATE  NITROGEN  IN  SOIL  GROWING  CORN  IN  1918:  SERIES  300, 
UNIVERSITY  NORTH  FARM 


Pounds  per  acre  in  2  million  pounds  of  surface  soil   (about  0  to 

water-free  basis 


inches), 


Plot 

Treatment 

Date  of  sampling 

Apparent 
utilization 
of 
nitrogen 
in  7  days 

June 
10 

June 
17 

June 
24 

July 
2 

July 
12 

Aug. 
2 

301 
302 
303 
304 
305 

None  

22.9 
22.7 
26.6 
62.0 
28.9 

34.8 
52.6 
32.6 
66.3 
33.0 

30.2 
47.8 
38.0 
48.9 
33.0 

28.2 
26.0 
22.2 
16.8 
15.9 

30.3 
40.0 
29.9 
20.7 
15.6 

26.8 
29.3 
21.1 
19.3 
27.9 

2.0 
21.8 
15.8 
32.1 
17.1 

R  

M  

RL  

ML  

306 
307 
308 
309 
310 

RLP  

63.6 
19.0 
55.8 
28.8 
90.7 

97.0 
34.4 
63.5 
29.4 
96.6 

61.5 
33.9 
49.1 
43.6 
81.5 

21.4 
23.0 
21.5 

27.2 
42.9 

16.0 
23.5 
16.5 
20.4 
30.2 

22.7 
22.0 
20. 
16.2 
20.8 

40.1 
10.9 
27.6 
16.4 
38.6 

MLP  

RLPK  

MLPK  

MxLPx  

TABLE  8. — INCREASES  OF  NITRATE  NITROGEN  ON  RESIDUES  PLOTS  (SWEET  CLOVER) 

AS  COMPARED  WITH  MANURE  PLOTS,  SOIL  GROWING  CORN  IN  1918: 

SERIES  300,  UNIVERSITY  NORTH  FARM 

Pounds  of  nitrogen  per  acre 


Plots 
com- 
pared 

Treatments 

Date  of  sampling 

June 
10 

June 
17 

June 
24 

July 
2 

July 
12 

Aug. 
2 

302:303 
304:305 
306:307 
308:309 

R  over  M  

-3.9 
33.1 
44.6 
27.0 

20.0 
33.3 
62.6 
34.1 

9.8 
15.9 
27.6 
5.5 

3.8 
.9 
-2.6 
-5.7 

10.1 
5.1 
-7.5 
-3.9 

8.2 
-8.6 
.7 
3.8 

RL  over  ML  

RLP  over  MLP  

RLPK  over  MLPK  

TABLE  9. — MOISTURE  CONTENT  OP  THE  SOIL  GROWING  CORN  IN  1918:  SERIES  300, 
UNIVERSITY  NORTH  FARM 

Tons  of  water  with  2  million  pounds  of  surface  soil   (about  0  to  6J3  inches),  water-free  basis 


Plot 

Treatment 

Date  of  sampling 

June 
10 

June 
17 

June 
24 

July 
2 

July 
12 

Aug. 
2 

301 
302 
303 
304 
305 

None  

224.4 
242.7 
246.4 
263.8 
268.8 

222.4 
230.9 
240.0 
245.5 

257.8 

220.1 
237.6 
225.0 
253.9 
256.0 

351.8 
357.7 
387.9 
284.0 
324.4 

224.2 
239.3 
243.8 
251.7 
262.3 

138.1 
149.4 
145.2 
157.  f 
151.3 

R  

M  

RL  

ML  

306 
307 
308 
309 
310 

RLP.. 

267.5 
270.0 
263.2 
280.8 
309.0 

255.6 
255.3 
253.6 
265.2 
279.5 

253.7 
250.1 
249.1 

247.8 
268.5 

371.4 
390.8 
378.4 
340.7 
329.4 

253.1 
252.5 
259.7 
268.4 
298.9 

165.8 
161.5 
159.4 
165.2 
177.5 

MLP  

RLPK  

MLPK  

MxLPx  

40  BULLETIN  No.  225  [March, 

soil  treatment,  such  as  residues,  limestone,  and  phosphorus,  and  they 
also  returned  the  highest  nitrate  production  from  the  sweet  clover. 

The  residues  plot  shows  rather  large  increases  over  the  check  plot 
in  nitrate  production,  altho  the  amount  of  green  material  turned  un- 
der was  small  compared  with  that  on  Plots  304,  306,  308,  and  310. 

Limestone  was  responsible  for  some  increases  in  nitrate  in  the 
early  periods.  Phosphorus  in  addition  to  residues  and  limestone  is 
responsible  for  the  maximum  results.  The  results  on  Plot  310  are 
derived  from  a  combination  of  manure  and  sweet  clover  and  ho  of 
course  are  not  to  be  considered  with  these  other  comparisons. 

These  figures  show  how  soil  treatment  can  influence  the  rate  and 
amount  of  nitrate  stored  up  for  the  critical  period  of  a  crop,  and  they 
lend  further  emphasis  to  statements  on  the  first  page  of  the  intro- 
duction. Further  investigation  along  these  lines  are  very  essential, 
as  this  particular  study  represents  only  one  season,  altho  it  does  in- 
clude four  comparisons. 

The  nitrate  removed  in  seven  days  is  given  in  the  ninth  column 
of  the  table  and  demonstrates  in  a  very  clear  manner  the  value  of 
sweet  clover  in  meeting  the  demands  of  rapidly  growing  crops.  These 
figures  coincide  with  those  showing  the  rate  of  growth  and  the  color 
of  the  crop  observed  during  this  period  and  later.  It  will  be  observed 
that  both  limestone  and  phosphorus  on  the  residues  plots  were  as- 
sociated with  a  large  assimilation  of  nitrate  during  the  seven-day 
period.  The  figures  for  the  manure  plots  are  much  lower  than  for 
the  residues  plots ;  it  appears  that  the  crop  was  using  nitrate  from 
the  manure  plots  much  more  slowly  and  over  a  longer  period. 

NITRATE  NITROGEN  IN  SOIL  GROWING  WHEAT  IN  1915-1916 
SERIES  200,  UNIVERSITY  NORTH  FARM 

A  nitrate  study  of  soil  on  which  winter  wheat  is  growing  involves 
a  set  of  conditions  different  from  those  present  with  crops  such  as 
corn,  soybeans,  or  even  oats.  There  must  be  a  supply  of  nitrates  for 
fall  growth,  and  nitrate  production  must  be  rapid  and  early  enough 
to  satisfy  the  spring  growth.  Soil  that  is  growing  wheat  can  hardly 
be  expected  to  accumulate  a  large  reserve  of  nitrate,  as  happens  in 
the  case  of  soil  in  preparation  for  corn,  because  the  wheat  crop  is 
drawing  heavily  on  the  supply  that  would  otherwise  accumulate  dur- 
ing May  and  a  part  of  June. 

It  is  therefore  essential  that  the  wheat  be  started  with  a  plentiful 
supply  of  nitrate  in  the  fall,  and  if  this  is  done  less  loss  will  result 
from  leaching,  owing  to  the  protection  afforded  by  good  plant  growth, 
and  more  nitrate  will  be  available  to  meet  the  critical  period  in  spring. 
This  can  be  accomplished  if  the  total  active  organic  matter  of  the 
soil  is  kept  at  a  high  figure.  Plowing  as  early  as  possible  is  to  be 


1920]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  41 

recommended,  especially  if  no  green-manure  crop  is  to  be  turned  un- 
der, as  it  saves  moisture  and  stores  up  nitrates.  In  most  seasons  the 
rainfall  during  July,  August,  and  a  part  of  September  is  not  the  cause 
of  serious  losses  of  nitrate. 

Soybeans  were  grown  on  this  series  in  1915  and  were  removed 
on  September  22.  Limestone  was  applied  en  September  29  and  the 
wheat  seeded  September  30.  This  series,  except  Plot  210,  gained  in 
nitrate  until  November  23  in  spite  of  the  demands  of  the  wheat.  The 
fall  rains  were  very  small,  and  no  losses  of  nitrate  resulted.  The  lime- 
stone and  residues  plots  appear  to  have  started  out  with  the  larger 
amounts  of  nitrates. 

The  results  presented  in  Table  10  show  that  this  series  was  effi- 
ciently supplying  nitrates  for  the  fall  growth  of  the  wheat  and, 
at  the  same  time,  that  the  nitrate  production  in  most  cases  actually 
increased ;  it  decreased  only  a  very  little  ori  Plot  210,  where  the  larg- 
est growth  occurred.  It  is  difficult  to  tell  whether  a  loss  from  rainfall 
occurred  before  March  18,  but  such  would  seem  to  be  the  case,  as  the 
total  precipitation  of  the  winter,  December  9  to  March  18,  was  only 
9.93  inches.  It  is  however,  evident  that  the  soil  was  able  to  meet  the 
needs  of  the  crop  and  even  to  gain  rapidly  up  to  May  4,  after  which 
time  the  demands  of  the  crop  materially  reduced  the  amount  of 
nitrate  present. 

The  large  use  of  nitrate  by  the  wheat  crop  occurred  during  the 
period  May  4  to  June  21.  The  true  nitrate-producing  capacity  is 
shown  in  the  period  after  the  wheat  had  been  removed  and  before  the 
sweet  clover  had  made  scarcely  any  growth.  The  amounts  of  nitrate 
found  on  this  series  in  August,  September,  and  November  indicate 
the  value  of  residues,  manure,  limestone,  and  phosphorus,  especially 
the  latter,  in  increasing  nitrate  production.  The  effect  of  limestone, 
which  was  applied  in  1915,  is  pronounced  on  certain  plots  on  this 
series.  The  reason  for  manure  assuming  a  higher  value  than  residues 
is  that,  contrary  to  the  general  practice,  a  light  application  was  made 
as  a  top-dressing  on  the  wheat  in  the  spring. 

In  twenty-nine  days  (May  4  to  June  2)  only  14.5  pounds  of 
nitrates  were  used  on  the  check  plot,  10.9  pounds  on  the  residue  plot, 
16.7  pounds  on  the  manure  plot,  37  pounds  on  the  residue-limestone 
plot,  2.7  pounds  on  the  residue-limestone-phosphorus  plot,  and  3.0 
pounds  on  the  manure-limestone-phosphorus  plot  (extra-heavy  treaf- 
ment).  These  are  very  small  decreases  compared  with  the  amounts 
found  for  the  corn  the  same  year,  in  only  eleven  days.  This  serves 
to  show  that  the  wheat  had  taken  up  considerable  nitrate  in  the  fall 
and  early  spring,  and  was  now  taking  it  very  gradually  compared 
with  a  crop  like  corn.  The  amounts  shown  for  Plots  206  and  210 
mean  very  little,  as  the  growth  of  the  crop  was  apparently  keeping 
the  supply  of  nitrate  rather  low,  while  the  other  plots  lacking  in  phos- 
phorus were  not  demanding  so  much. 


42 


BULLETIN  No.  225 


[March, 


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1920]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  43 


This  series  was  in  corn  in  1916.  The  soil  was  disked  March  26. 
Wheat  straw  was  applied  to  the  residues  plots  after  the  oats  were 
seeded.  This  was  done  because  of  the  necessity  of  turning  under  on 
Series  500  the  residues  produced  on  Series  100,  where  the  alfalfa 
had  been  seeded  after  having  occupied  Series  500  for  five  years. 

Attention  is  called  to  the  fact  that  this  series,  the  second  year 
after  alfalfa  roots  were  plowed  under,  supported  yields  as  high  as 
104.7  bushels  of  oats  and  ended  with  about  10  pounds  of  nitrate  in 
spite  of  the  fact  that  a  small  growth  of  clover  was  present. 

No  such  sudden  marked  decreases  in  nitrate  production  occurred 
with  the  oat  crop  as  were  observed  with  the  corn  crop.  The  de- 
creases came  between  May  19  and  July  7,  altho  here  again  decreases 
were  observed  on  the  better  plots  at  earlier  dates.  It  is  well  to  note 
that  the  best  plots  were  maturing  faster,  and  usually  reduced  the 
supply  of  nitrates  one  to  two  weeks  sooner,  than  the  poorer  plots. 
This  was  true  with  the  wheat  and  corn  crops,  as  noted  in  the  previous 
series. 

The  relatively  low  amount  of  nitrate  nitrogen  remaining  in  the 
soil  after  a  crop  like  oats  or  wheat  has  been  removed,  is  important 
to  note,  particularly  when  clover  is  on  the  land  during  a  hot,  dry 
period  such  as  commonly  exists  in  Illinois  during  July,  August,  and 
often  September.  The  legume  undoubtedly  draws  on  the  atmospheric 
nitrogen,  if  it  makes  any  appreciable  growth,  for  nitrates  may  not 
accumulate  under  these  conditions  to  any  marked  extent,  even  in 
the  good  soils,  until  late  in  September  or  early  in  October. 

The  capacity  of  this  series  to  produce  nitrate  should  be  carefully 
considered,  as  the  crop  yields  are  high.  Good  soil  treatment  and 
a  good  crop  rotation  are  practiced.  The  problem  of  a  balance  of 
nutrients  seems  best  solved  on  Plot  506,  while  on  Plot  510  there  is 
another  example  of  an  uneconomical  use  of  nitrogen  as  compared  with 
Bother  elements  of  plant  food. 

Looking  at  the  figures  for  1917  (Table  12),  it  is  at  once  apparent 
that  a  considerable  loss  of  nitrates  occurred  between  March  10  and 
March  22.  The  average  loss  per  plot  amounted  to  24.5  pounds,  the 
plots  possessing  the  smallest  amounts  of  nitrate  losing  the  least,  and 
those  possessing  the  largest  amounts  losing  the  most.  A  rainfall  of 
three  inches  which  occurred  during  this  period  (2.93  inches  on  one 
day),  before  the  land  was  disked,  was  responsible  for  this  large  loss. 
It  is  the  most  striking  loss  due  to  rain  which  was  encountered  in  the 
four  years  of  sampling  on  these  series.  It  is  interesting  to  note  that 
the  corn  stalks,  in  two  of  the  three  cases  in  which  they  were  used, 
appear  to  have  checked  the  loss.  The  losses  of  nitrate,  expressed  in 
percentage  of  the  total  nitrate  nitrogen  present,  are  given  in  Table  14. 


44 


BULLETIN  No.  225 


[March, 


TABLE  12. — NITRATE  NITROGEN  IN  SOIL  GROWING  OATS   IN  1917:  SERIES  500, 
UNIVERSITY  NORTH  FARM 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6^5  inches), 
water-free  basis 


Plot 

Treat- 
ment 

Date  of  sampling 

Oat 
yield, 
bu. 

Mar. 
10 

Mar. 
22 

Apr. 
10 

Apr. 
20 

May 
10 

May 
19 

June 
18 

July 

7 

501 
502 
503 
504 
506 
510 

None  

42.3 
38.4 
42.2 
51.2 
36.7 
58.8 

16.9 
19.3 
13.7 
26.3 
19.4 
26.9 

26.6 
24.5 
28.4 
32.3 
27.7 
29.0 

32.0 
24.7 
27.1 
25.1 
29.7 
29.5 

25.2 
20.1 
27.7 
18.7 
16.8 
18.4 

31.4 
30.2 
26.6 
22.0 
16.9 
8.0 

15.6 
13.5 
11.4 
10.5 
12.1 
12.2 

8.1 
8.8 
9.0 
7.4 
8.6 
10.0 

83.1 
87.2 
93.1 
81.6 
104.7 
85.6 

R  

M  

RL  

RLP  

MxLPx.  .. 

TABLE  13. — MOISTURE  CONTENT  OF  THE  SOIL  GROWING  OATS  IN  1917:  SERIES  500, 
UNIVERSITY  NORTH  FARM 

Tons  of  water  with  2  million  pounds  of  surface  soil  (about  0  to  62/$  inches),  water-free  basis 


Plot 

Treat- 
ment 

Date  of  sampling 

Mar. 
10 

Mar. 
22 

Apr. 
10 

Apr. 
20- 

May 
10 

May 
19 

June 
18 

July 

7 

501 
502 
503 
504 
506 
510 

None.  .  .  . 
R  

193.4 
182.9 
196.9 
167.4 
187.3 
171.4 

306.9 
317.1 
314.3 
301.5 
325.6 
302.4 

291.1 
286.7 
292.5 
282.9 
291.1 
282.7 

297.5 
315.9 
300.2 
302.8 
314.8 
299.2 

282.3 
296.5 
283.6 
284.9 
301.6 
276.5 

238.9 
259.6 
228.6 
248.8 
256.2 
177.4 

265.8 
286.8 
269.5 
276.0 
293.1 
256.3 

205.7 
237.7 
194.9 
231.0 
220.5 
205.6 

M  

RL  

RLP.  .  .  . 
MxLPx.. 

TABLE  14. — EFFECT  OF  RESIDUES  IN  PREVENTING  LOSSES  OF  NITRATE 


Plot 

Treatment 

Percentage  of  nitrate  lost 

501 

Nothing  

60.0 

502 

Residues,  corn  stalks  

49.7 

503 

Manure  

67.5 

504 

Residues,  corn  stalks  

48.6 

506 

Residues,  corn  stalks  

47.1 

510 

Manure  

54.2 

These  losses  demonstrate  the  desirability  of  organic  matter  in 
/the  soil,  and  they  indicate  quite  clearly  what  would  happen  to  nitrate 
'applied  as  sodium  nitrate.  It  is  not  known  how  much  of  this  nitrate 
passes  out  into  the  drains ;  only  the  lysimeters  will  answer  this  ques- 
tion for  Illinois  conditions. 

The  rate  of  growth  of  the  crop  is  shown  by  the  almost  com- 
plete cessation  of  nitrate  accumulation  on  Plot  510  during  the  period 
from  March  22  to  May  10,  with  an  increase  on  all  others.  A  further 
increase  to  May  19  and  then  a  decrease  to  July  7  is  apparent. 

The  amount  of  nitrogen  removed  during  the  thirty  days  from 
May  19  to  June  18  may  well  be  compared  with  that  removed  by  the 
wheat  and  corn  crops. 


19SO]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  45 

SOME  IMPORTANT  FACTS  SHOWN  BY  DATA  FROM  THE 
UNIVERSITY  NORTH  FARM 

CORN  CROP 

Some  important  facts  derived  from  the  four  years  study  on  the 
University  North  Farm  are  briefly  summarized  below: 

A  large  amount  of  nitrate  was  removed  by  the  corn  crop  in 
a  very  few  days  at  the  time  it  was  laid  by,  which  was  between  June 
25  and  July  10.  This  occurrence  was  first  observed  on  Series  400, 
in  1915;  it  has  been  noted  in  each  succeeding  year  on  all  series. 
The  amount  removed  was  lowest  in  1917,  when  soft  corn  was  abundant. 
This  crop  uses  heavily  of  nitrate,  if  it  is  available,  and  consequently 
the  high  nitrate-producing  plots  show  the  largest  decreases,  and  what 
is  more  important,  these  decreases  occurred  at  earlier  dates.  A  more 
rapid  crop  growth  always  is  observed  on  these  plots. 

The  high  nitrate  content  of  Series  500  in  1916  is  traceable  to 
the  presence  of  alfalfa  roots  and  to  the  protective  action  of  a  crop 
which  occupies  the  land  continuously.  By  comparing  this  series  with 
Series  200  in  1916,  which  was  in  wheat,  it  is  seen  that  Series  500 
was  much  more  efficient  in  nitrate  production.  The  residues  plots 
show  a  decided  superiority  over  the  manure  plots  in  this  series  (500). 

The  effect  of  phosphorus  in  increasing  nitrates  is  observable 
between  July  14  and  September  14,  after  the  influence  of  the  crop 
had  about  disappeared.  Limestone  produced  only  a  slight  increase 
in  nitrates.  The  effect  of  the  alfalfa  roots  in  causing  a  general  in- 
'  crease  in  nitrate  production  over  the  whole  series  was  to  reduce  the 
differences  that  might  otherwise  have  appeared  from  the  applications 
of  limestone  and  phosphorus. 

On  Series  200  in  1917  nitrate  production  was  somewhat  lower 
than  usual,  as  shown  by  the  smaller  amounts  of  nitrogen  taken  up  in 
the  twelve-day  period  covering  the  time  at  which  the  corn  was  laid 
by ;  and  the  rate  of  growth  of  the  corn  was  slower.  The  highest  nitrate 
production  was  associated  with  limestone  and  phosphorus  treatments ; 
especially  was  this  true  at  the  most  critical  periods  of  crop  growth. 
Series  500,  even  tho  in  oats,  contained  larger  amounts  of  nitrate  than 
Series  200,  again  indicating  a  residual  influence  on  the  part  of  the* 
alfalfa  roots. 

On  Series  300  in  1918  the  most  valuable  results  were  obtained. 
Sweet  clover  as  a  green  manure  plowed  under  for  corn  surpassed 
stable  manure  in  nitrate  production,  from  two  to  three  times.  The 
amount  of  nitrate  used  shows  a  positive  relationship  to  the  presence 
of  residues  (sweet  clover)  and  the  additional  effect  of  limestone  and 
phosphorus.  The  figures  from  this  series  show  the  value  of  sweet 
clover  as  compared  with  no  treatment,  the  added  value  of  limestone, 


46  BULLETIN  No.  225  [March, 

and  the  still  greater  increase  resulting  from  applications  of  phos- 
phorus. The  results  are  too  clear  to  need  further  explanation  (see 
Plot  306,  Table  7) .  Field  observations  as  to  height  of  stalks  and  color 
of  growth  were  in  accord  with  the  differences  in  nitrate  reported 
between  the  sweet-clover  plots  and  the  manure  plots. 

WHEAT   CROP 

A  careful  study  from  the  time  of  the  seeding  of  the  wheat  to 
some  time  after  harvesting  it — in  all,  about  fourteen  months — fur- 
nishes valuable  information  regarding  the  time  at  which  this  crop 
demands  the  most  nitrate.  On  Series  200  in  1915  the  soil  not  only 
supported  the  fall  growth  of  wheat  but  constantly  increased  in  nitrate 
content  until  late  November,  decreasing  only  slightly  in  December. 

Land  growing  wheat  holds  the  nitrate  at  a  lower  level  than  land, 
in  preparation  for  corn  or  soybeans,  which,  unless  supporting  a  catch 
crop,  in  reality  is  fallow  until  about  the  last  of  May  or  middle  of 
June,  according  to  the  crop.  The  wheat  on  this  series  reduced  the 
nitrates  very  materially  in  the  month  of  May ;  which  time  coincides 
with  the  period  during  which  the  wheat  plant  develops  its  leaves 
and  approaches  maturity.  After  the  removal  of  the  wheat  crop,  the 
plots  on  this  series  receiving  manure,  residues,  limestone,  and  phos- 
phorus showed  definite  increases  in  nitrates. 

Phosphorus,  as  in  other  series,  was  again  superior  to  limestone 
for  nitrate  production.  In  the  case  of  the  wheat,  the  best  nitrate- 
producing  plots  supported  the  most  rapid  growth,  and  the  crop  be- 
gan reducing  the  nitrate  supply  on  them  earlier  than  on  the  poorer 
plots.  Concerning  this  fact  we  see  an  analogy  with  the  corn  crop. 

OAT  CROP 

The  studies  conducted  with  oats  occupying  the  land  (Series 
500  in  1917)  are  valuable  in  showing  how  rainfall  may  be  the  cause 
of  a  series  loss.  Oats  occupy  the  land,  in  a  rotation  of  this  kind,  at 
a  period  when  the  nitrate  is  produced  in  the  smallest  amounts,  it 
having  been  reduced  by  the  preceding  corn  crop.  In  this  particular 
case,  however,  the  influence  of  the  alfalfa  roots  seems  to  have  ex- 
tended over  more  than  one  year,  as  very  high  nitrate  production 
was  found  in  March,  1917,  the  alfalfa  stubble  having  been  plowed 
under  in  March,  1916.  On  all  but  two  plots  the  rate  of  production  was 
insufficient  to  cause  an  increase,  but  that  it  met  the  demands  of 
the  rapidly  growing  crop  on  all  plots  is  shown  by  the  yield  and  the 
surplus  even  as  late  as  July  7.  It  should  be  remembered  also  that 
clover  was  in  the  oats,  and  the  clover  may  have  drawn  on  the  nitrate 
to  a  small  extent. 


1920]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  47 

As  with  wheat,  the  oat  crop  required  most  of  its  nitrate  in  late 
May  and  early  June.  The  soil  has  only  a  slight  chance  to  build  up 
a  reserve  ahead  of  this  crop,  in  the  spring,  but  it  may  do  so  in  the 
previous  fall. 

The  growth  of  the  oats  was  most  rapid  on  the  plots  with  the 
highest  nitrate.  As  with  corn  and  wheat,  the  best  nitrate-producing 
plots  furnished  the  largest  amount  of  nitrate  to  the  crop  and  did 
it  at  an  earlier  period  than  the  others. 

EFFECT    OF    SOIL    TREATMENT    AND    OF    CROPPING 
SYSTEMS   ON  NITRATE   PRODUCTION 

UNIVERSITY  SOUTH  FARM  AT.URBANA 

The  rotations  conducted  on  the  South  Farm  afford  excellent 
opportunity  to  study  the  effect  of  a  green  manure,  rock  phosphate, 
limestone,  and  the  rotation  itself  on  nitrate  production,  especially 
in  regard  to  the  sequence  of  the  crops. 

These  rotations  represent  conditions  similar  to  those  found  on 
the  average  farm  where  limestone  and  rock  phosphate  are  applied. 
The  applications  are  made  here  according  to  the  recommendations 
of  the  Experiment  Stati6n  for  general  farm  practice.  Raw  rock 
phosphate  is  applied  with  stable  manure  and  in  conjunction  with 
crop  residues  and  green  manures,  such  as  red  clover.  The  applica- 
tion of  phosphate  is  made  at  the  rate  of  one  ton  per  acre  once  in 
four  years,  and  is  plowed  under  with  crop  residues,  green  manure, 
or  stable  manure,  depending  upon  the  system  of  farming. 

In  the  northwest  and  southwest  rotations  limestone  is  applied 
at  the  rate  of  two  tons  per  acre,  once  in  four  years,  on  the  east  half 
of  all  but  the  check  plots ;  but  no  limestone  is  applied  in  the  north- 
central  and  south-central  rotations. 

While  these  results  are  for  one  season  only,  they  represent  a 
large  number  of  analyses  and  many  tests  of  the  same  kind.     One  • 
season's  nitrate  studies  or  even  a  few  analyses,  if  the  samples  are 
taken  at  the  critical  or  proper  time,  are  very  valuable,  especially 
for  such  crops  as  wheat,  oats,  corn,  and  soybeans.    The  figures  which 
follow  are  the  result  of  many  averages,  for  space  limitations  would, 
make  practically  impossible  the  presentation  of  detailed  figures.    The 
manner  of  conducting  the  work  this  year  permits  of  averaging  the  re- 
sults, which  were  more  alike  in  nature  than  those  obtained  on  the 
North  Farm. 

Table  15  shows  the  sequence  of  the  crops  in  the  various  rotations, 
the  series  selected  for  sampling,  the  crops  growing  on  them,  and  the 
soil  treatment  of  the  various  plots. 

In  the  northwest  rotation  only  the  live-stock  system  is  practiced, 
altho  a  cover  crop  is  seeded  in  the  corn  to  be  plowed  under  for  soy- 


48 


BULLETIN  No.  225 


[March, 


beans,  thus  making  possible  a  comparison  of  four  plots  of  each  treat- 
ment in  the  100  and  400  series 


TABLE  15. — SERIES  SELECTED  FOR  SAMPLING:  UNIVERSITY  SOUTH  FARM,  1918 


Rotations 

Series  sampled 
and  crops 
occupying 
them 

Plots 
sampled 

Treat- 
ment 

Location 

Crop  sequence 

Northwest2 

Potatoes,  corn,  soybeans, 
and  alfalfa  (7  years) 

100:  Soybeans 
400:  Corn 

146 
149 
150 
153 

446 
449 
450 
453 

MLpi 
M 
M 
MLP1 

Southwest2 

Wheat  (red  clover),  corn, 
oats,  and  clover  or  soybeans 

100:  Soybeans 
300:  Corn 

166 
169 
170 
173 

366 
369 
370 
373 

RLP1 
R 
M 
MLP1 

North  Central3 

Corn,  corn,  oats,  and 
clover  (or  soybeans) 

600:  Clover 
800:  Corn 

646 
649 
650 
653 

846 
849 
850 
853 

RP 
R 
M 
MP 

South  Central3 

Corn,  corn,  corn,  soybeans 

500:  Corn 
600:  Soybeans 

566 
569 
570 
573 

666 
669 
670 
673 

RP 
R 

M 
MP 

limestone  applied  only  to  east  half  of  plots  in  northwest  and  southwest 
rotations. 

"Indicated  as  good  rotations  in  Tables  22  and  23. 
'Indicated  as  poor  rotations  in  Tables  22  and  23. 

Except  in  the  northwest  rotation,  the  manure  used  in  these  rota- 
tions is  in  proportion  to  the  dry  weight  of  the  crops  produced;  in 
the  northwest  rotation  a  very  heavy  application  (40  tons  per  acre) 
is  made.  Crop  residues  are  returned  as  on  the  North  Farm.  On 
the  southwest  rotation,  red  clover  is  seeded  in  the  wheat  as  a  cover 
crop,  to  be  plowed  under  green  the  following  spring  for  corn.  The 
data  afford  the  following  comparisons  of  soil  treatment: 

Eesidues  (red  clover  plowed  under  green)  compared  with  manure 

Eock  phosphate  compared  with  no  phosphorus 

Limestone  compared  with  no  limestone 

They  also  afford  comparisons  of  the  following  cropping  systems : 

Three  crops  rotating  with  seven  years  of  alfalfa.  Manure  applied, 
residues  removed,  but  a  green  manure  plowed  under  ahead  of 
soybeans 

Wheat  (red  clover  on  residues  plots),  corn,  oats,  and  soybeans  or 
clover 

Corn,  corn,  oats,  and  clover 

Corn,  corn,  corn,  and  soybeans 

The  same  methods  of  obtaining  samples  were  practiced  on  these 
plots  as  on  the  North  Farm,  with  the  exception  that  the  plots  were 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


49 


sampled  east  and  west  instead  of  north  and  south  and  the  number 
of  borings  was  fifteen  for  each  tenth-acre.  These  plots  are  one-fifth 
acre  each,  and  15  borings  obtains  a  very  reliable  sample  for  one- 
tenth  of  an  acre.  In  some  cases  30  borings  were  taken  per  tenth- 
acre  to  provide  for  special  comparison.  Often  four  determinations 
were  made  on  a  sample  in  order  to  test  the  method  and  the  plot 
variations.  On  the  North  Farm,  24  to  30  borings  were  made  for 
each  one-tenth  of  an  acre,  as  that  method  had  been  in  use  for  four 
years. 

Toluene  was  used  on  all  samples ;  it  was  placed  in  the  jars  ahead 
of  the  soil  while  in  the  field.  The  experience  of  this  laboratory  has 
been  that  some  such  preservative  is  even  more  necessary  than  is  com- 
monly thought ;  particularly  is  this  true  in  the  late  spring  and  early 
summer,  when  conditions  are  favorable  for  active  nitrate  production. 

The  results  of  the  studies  on  the  South  Farm  will  be  presented 
and  discussed  in  the  order  indicated  by  the  arrangement  shown  above. 

INFLUENCE  OF  GREEN  MANURE  AS  COMPARED  WITH  STABLE  MANURE 

As  soil  treatment  is  the  direct  as  well  as  the  underlying  cause 
of  most  of  the  differences  found,  it  will  be  considered  first. 

The  determinations  assembled  in  Table  16  show  the  influence 
of  a  green  manure  (legume)  plowed  under  in  the  spring  for  corn,  as 
compared  with  stable  manure.  In  this  case  the  legume  was  red 
clover.  In  most  of  the  data  presented  here,  only  the  results  up  to 
the  time  the  crop  was  laid  by  are  given,  as  after  that  period  the 
crops  themselves  may  interfere  with  a  true  comparison. 

TABLE  16. — EFFECT  OF  SOIL  TREATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 

RED  CLOVER  AS  A  GREEN  MANURE  COMPARED  WITH  STABLE  MANURE:    SOIL 

GROWING  CORN:    SERIES  300SW,  UNIVERSITY  SOUTH  FARM,  1918  . 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6?^  inches),  water-free  basis 


Plot 
(WH) 

Treatment 

Date  of  sampling 

June  10 

June  17 

June  24 

July  2 

369 
370 

Residues  (red  clover  plowed 
under  green  in  1918)  

82.59 
51.31 

79.41 
44.94 

"81.69 
62.23 

36.57 
23.95 

Manure   

Gain  for  green  manure  

31.28 

34.47 

19.46 

12.62 

366 
373 

Residues,  P  (red  clover  plowed 
under  green  in  1918)  

82.13 
55.58 

78.13 
56.67 

122.12 
52.94 

43.34 
29.43 

Manure,  P  '  

Gain  for  green  manure  

26.55 

21.46 

69.18 

13.91 

The  high  nitrate  production  is  the  result  of  the  green-manure 
crop.  The  results  need  no  further  explanation,  as  they  are  consistent 
thruout,  both  with  raw  rock  phosphate  and  without.  In  the  other 
series  studied  the  residues  plots  where  no  green  manure  is  used  were 


50 


BULLETIN  No.  225 


[March, 


slightly  inferior  to  the  manure  plots.  In  those  series,  however,  the 
crops  studied  were  farthest  removed  from  the  returned  residues  and 
the  manure,  which  condition  could  not  be  considered  as  satisfactory 
for  a  comparison  except  from  the  standpoint  of  the  residual  effects 
of  the  materials. 

INFLUENCE   OF   KAW   ROCK   PHOSPHATE 

In  studying  the  influence  of  raw  rock  phosphate  on  nitrate  pro- 
duction it  will  assist  in  an  understanding  of  some  of  the  data  con- 
cerning soil  treatment  if  the  soil  type  is  briefly  described. 

Series  100,  both  in  the  northwest  and  in  the  southwest  rotations, 
is  medium  brown  silt  loam,  while  Series  300  and  400  of  these  rota- 
tions are  a  very  heavy  phase  of  brown  silt  loam,  even  called  a  black 
clay.  Series  600,  in  the  north-central  rotation,  appears  to  be  lighter, 
or  more  nearly  like  Series  100.  The  other  series  are  rather  heavy 
brown  silt  loams,  and  Series  800,  in  the  main,  is  a  very  heavy  clay. 

The  influence  of  raw  rock  phosphate  in  Series  100  and  400  of  the 
northwest  rotation,  and  Series  100  of  the  southwest  rotation,  is  shown 
in  Table  17. 


TABLE  17. — EFFECT  OF  SOIL  TREATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 

ROCK  PHOSPHATE  COMPARED  WITH  No  PHOSPHATE:    CORN  AND  SOYBEANS 

SERIES  100,  400NW,  100SW,  UNIVERSITY  SOUTH  FARM,  1918 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6J3  inches),  water-free  basis 


Crop 

Plot 

(wy2) 

Treatment 

Date  of  sampling 

Gain  for 
phosphorus 

June  10 

June  17iJune  24 

Soybeans 

146,153 
149,150 

Manure,  P  

71.78 
70.36 

58.61 
56.13 

84.28 
70.09 

18.09 

Manure  

Soybeans 

166,173 
169,170 

Organic  matter,1  P.  .  . 
Organic  matter1  

42.08 
33.88 

40.64 
41.46 

46.61 
34.98 

19.01 

Corn 

446,453 
449,450 

Manure,  P  

65.56 
54.14 

58.93 
63.45 

60.85 
44.30 

23.45 

Manure  

aThe  term  ' '  organic  matter ' '  is  used  to  indicate  an  average  of  both  manure 
and  crop  residue  plots  in  this  series. 

The  gain  for  phosphorus,  in  the  form  of  raw  rock  phosphate, 
came  to  the  maximum  on  June  24  on  these  series.  This  was  to  be 
expected,  since  the  phosphate  was  applied  and  plowed  under  with 
the  organic  matter  in  May.  Some  time  is  required  to  gain  the  speed 
which  would  make  the  nitrate  measurable.  The  results  obtained 
on  the  residues  plots  of  Series  300  (corn,  1918),  where  the  green 
manure  was  plowed  under,  are  given  again  in  Table  18  in  order  to  show 
the  gains  resulting  from  the  presence  of  phosphorus. 

The  maximum  nitrate  production  occurred  in  this  series  on  June 
24,  which  is  the  same  date  on  which  maximum  production  was  found 
in  Series  100  and  400  of  the  northwest  rotation,  as  reported  above. 
The  figures  show  not  only  a  large  gain  for  phosphorus  in  the  form  of 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


51 


TABLE  18. — EFFECT  OF  SOIL  TKEATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 
ROCK  PHOSPHATE  COMPARED  WITH  No  PHOSPHATE:    SOIL  GROWING  CORN 

SERIES  300SW,  UNIVERSITY  SOUTH  FARM,  1918 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6%  inches),  water-free  basis 


Plot 

(wy2) 

Treatment 

Date  of  sampling 

Gain  for 
phosphorus 

June  10 

June  17 

June  24 

July  2 

366 
369 
370 
373 

Residues,1  P  

82.13 
82.59 
51.31 
55.58 

78.13 
79.41 
44.94 
56.67 

122.12 
81.68 
62.23 
52.94 

43.34 
36.57 
23.95 
29.43 

45.47 
12.19 

Residues1  

Manure  

Manure,  P  

JRed  clover. 

raw  rock  phosphate  but  also  the  superiority  of  the  green  manure  over 
the  stable  manure.  Plot  373,  receiving  stable  manure,  was  supporting 
a  very  large  growth,  and  that  fact  undoubtedly  accounts  for  its  low- 
ered value  on  June  24;  but  when  the  gains  here  are  compared  with 
the  gains  on  Series  400,  it  would  seem  that  there  is  little  question 
regarding  the  value  of  a  green  manure  nor  of  the  advisability  of  using 
raw  rock  phosphate  in  connection  with  rapidly  decaying  organic 
matter. 

The  nitrate  production  on  Series  600  is  shown  in  Table  19; 
here  the  influence  of  raw  rock  phosphate  is  shown  with  an  unculti- 
vated crop.  The  clover  was  sampled  after  the  first  crop  had  been 
cut  either  for  hay  or  for  seed.  The  lower  results  with  the  stable 
manure  are  perhaps  accounted  for  by  the  larger  crop  just  removed 
from  these  plots. 

TABLE  19. — EFFECT  OF  SOIL  TREATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 

ROCK  PHOSPHATE  COMPARED  WITH  No  PHOSPHATE:     SOIL  GROWING 

CLOVER:  SERIES  600NC,  UNIVERSITY  SOUTH  FARM,  1918 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to-  6 2/$  inches),  water- free  basis 


Plot 

Treatment 

Date  of  sampling 

Gain  for 
phosphorus 

June  24 

July  2 

July  12 

August  2 

646 
649 
650 
653 

Residues,  P. 
Residues  .  .  . 
Manure  .... 
Manure,  P.  . 

23.98 
20.63 
18.26 
29.19 

46.07 
11.60 
17.26 
32.92 

21.25 
15.82 
5.56 
18.12 

21.45 
19.12 
21.53 
23.04 

45.58 
40.66 

This  series  affords  a  very  good  comparison  of  nitrate  production  • 
in  the  presence  and  absence  of  raw  rock  phosphate,  for  a  crop  of 
clover  had  been  removed  before  the  first  samples  were  taken.  It 
appears  that  the  second  crop  of  clover  had  either  taken  up  all  its 
nitrate  by  July  12  or  that  the  soil  was  accumulating  nitrate  above 
that  used  by  this  legume. 

The  influence  of  raw  rock  phosphate,  on  the  west  half  of  all  the 
series  growing  corn  is  shown  in  Table  20,  and. similar  data  occur  in 
Table  21  for  soybeans  and  clover.  These  data  are  averages  of  an 
equal  number  of  plots  from  the  good  and  the  poor  cropping  systems. 


52 


BULLETIN  No.  225 


[March, 


This  means  that  on  some  of  the  plots  included  in  the  averages  the 
corn  crop  was  farthest  removed  from  the  applications  of  manure  and 
crop  residues. 

To  show  the  importance  of  detailed  study  in  presentation  of  the 
results,  Tables  20  and  21,  summarizing  all  results  for  corn  and  soy- 
beans, are  first  introduced,  and  then  further  and  more  detailed 
analysis  of  the  data  is  shown  in  Table  22,  -where  the  results  of  appli- 
cations of  raw  rock  phosphate,  manure,  and  green  manure,  made  in 
1918  on  the  corn  series  in  the  rotations  of  good  crop  sequence,  are 
compared  with  those  secured  from  rotations  of  poor  crop  sequence, 
or  where  the  crop  is  farthest  removed  from  the  soil  treatment. 

TABLE  20. — EFFECT  OF  SOIL  TREATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 

RAW  ROCK  PHOSPHATE  COMPARED  WITH  No  PHOSPHATE 

ALL  CORN  SERIES,  UNIVERSITY  SOUTH  FARM,  1918 

(West  halves  of  plots) 
Pounds  per  acre  in  2  million  pounds  of  surface    soil  (about  0  to  6^  inches),  water-free  basis1 


Treatment 

Date  of  sampling 

June  10 

June  17 

June  24 

July  2 

Organic  matter,  P  

54.40 

47.37 

58.36 

25.01 

Organic  matter  

45.88 

45.21 

46.54 

32.52 

JEach  figure  represents  the  average  of  the  analyses  of  eight  plots. 

TABLE  21. — EFFECT  OF  SOIL  TREATMENT  ON  PRODUCTION  OF  NITRATE  NITROGEN 

RAW  ROCK  PHOSPHATE  COMPARED  WITH  No  PHOSPHATE 
ALL  SOYBEAN-CLOVER  SERIES,  UNIVERSITY  SOUTH  FARM,  1918 

(West  halves  of  plots) 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  62/$   inches),  water-free  basis1 


.treatment 

June  10 

June  17 

June  24 

July  2 

Organic  matter,  P  

51.51 

41.95 

45.64 

27.46 

Organic  matter  

49.99 

42.50 

27.14 

34.25 

'Each  figure  represents  the  average  of  the  analyses  of  eight  plots. 

These  results  show  very  clearly  the  value  of  good  rotations  in 
connection  with  the  use  of  raw  rock  phosphate.  The  differences  in 
these  rotations  lie  in  the  crop  sequence  and  in  the  use  of  green  and 
stable  manures.  The  greater  differences  between  the  good  and  poor 
rotations  of  the  corn  series  than  between  the  good  and  poor  rotations 
of  the  soybean  series  may  be  accounted  for  by  the  fact  that  the  soy- 
beans occupied  the  series  that  are  at  the  poorer  places  in  all  rotations 
and  had  been  preceded  by  proportionately  larger  crops  in  the  good 
rotations  than  in  the  poorer  rotations.  This  is  where  they  should 
occur,  since  they  are  not  dependent  upon  nitrates  as  a  source  of 
nitrogen. 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


53 


TABLE  22. — EFFECT  OF  CROPPING  SYSTEMS  ON  PRODUCTION  OF  NITRATE  NITROGEN 

GOOD  ROTATIONS  COMPARED  WITH  POOR  ROTATIONS 
RAW-ROCK-PHOSPHATE^PLOTS,  UNIVERSITY  SOUTH  FARM,  1918 

(West  halves  of  plots) 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  &%  inches)  water-free  basis1 


Rotation 

Plot 

Date  of  sampling 

June  10 

June  17     |     June  24     | 

July  2 

CORN 


Good  

366,373 

67.21 

63.17 

74.19 

37.97 

446,453 

Poor  

566,573 

41.59 

31.57 

42.54 

19.55 

846,853 

SOYBEANS 


Good  

146,153 

56.92 

49.62 

65.44 

32.24 

166,173 

Poor.  

646,653 

40.69 

26.55 

28.  572 

29.91 

666,673 

1Each  figure  represents  the  average  of  the  analyses  of  four  plots. 
2Average  includes  clover  series. 

The  data  in  Table  23  serve  to  indicate  the  important  influence 
exerted  by  the  rotation  on  the  results  which  will  be  derived  from  a 
given  soil  treatment. 

TABLE  23. — EFFECT  OF  CROPPING  SYSTEMS  ON  PRODUCTION  OF  NITRATE  NITROGEN 

GOOD  ROTATIONS  COMPARED  WITH  POOR  ROTATIONS 
ORGANIC-MATTER  PLOTS,  UNIVERSITY  SOUTH  FARM,  1919 

(Whole  plots) 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6%  inches)  water-free  basis1 


Rotation 

Plots 

Dates  of  sampling 

June  10 

June  17     j     June  24 

July  2 

CORN 


Good  

369,370 

62.42 

56.14 

54.02 

34.85 

449,450 

Poor  

569,570 

32.38 

30.48 

35.82 

23.02 

849,850 

SOYBEANS 


Good  

149,150 

54.62 

48.31 

63.37 

36.52 

169,170 

Poor  

649,650 

43.65 

26.43 

24.  952 

23  .  072 

669,670 

figure  represents  the  average  of  the  analyses  of  eight  plots. 
*Averages  include  clover  series. 

EFFECT  OF  LIMESTONE  ON  NITRATE  PRODUCTION 

The  influence  of  limestone  on  nitrate  production,  where  calcium 
is  needed  by  crops  or  where  a  less  acid  soil  is  necessary  in  order  to 
promote  bacterial  action,  has  been  well  established. 


54 


BULLETIN  No.  225 


[March, 


The  results  of  the  studies  on  the  South  Farm  did  not  indicate  a 
consistent  increase  for  limestone  over  the  natural  variations  in  the 
plots.  On  the  plots  receiving  limestone,  raw  rock  phosphate,  and  resi- 
dues, and  on  the  plots  receiving  limestone,  raw  rock  phosphate,  and 
manure,  limestone  increased  the  nitrate  in  some  cases,  but  the  effect 
did  not  hold  thruout. 

Series  300  and  400  are  on  a  different  type  of  soil  from  Series  100 
and  200  and  they  are  not  in  need  of  limestone  as  yet;  which  fact 
accounts  for  no  increases  of  nitrate  being  found.  However,  the 
hidden  benefit  of  limestone  in  causing  a  greater  production  of  green 
manure  must  not  be  ignored. 


If  all  the  results  of  all  the  series  in  each  of  the  four  crop  systems 
are  arranged  as  shown  in  Table  24,  it  will  be  seen  that  the  rotation 
potatoes,  corn,  soybeans,  and  alfalfa  is  the  richest  in  nitrates.  This  is 
to  be  expected,  as  large  applications  of  stable  manure  are  made  for 
the  potato  crop  and,  in  addition  to  this,  in  1918  a  green-manure 
crop  (sweet  clover)  was  plowed  under  for  the  soybeans. 

The  rotation  wheat,  corn,  oats,  and  clover  or  soybeans,  in  which 
the  effect  of  red  clover  as  a  green  manure  and  the  effect  of  stable 
manure  are  averaged,  is  very  nearly  as  good  as  the  rotation  men- 
tioned above,  especially  at  the  period  when  these  crops  required  the 
most  nitrate. 

The  rotations  corn,  corn,  oats  and  clover,  and  corn,  corn,  corn, 
and  soybeans,  while  occupying  at  least  as  good  soil  as  any  of  the  rota- 
tions and  on  most  series  the  better  part  of  the  field  originally,  are 
decidedly  inferior  owing  to  the  sequence  of  the  crops  in  the  rotation. 

TABLE  24. — INFLUENCE  OP  DIFFERENT  CROPPING  SYSTEMS  ON  PRODUCTION 
OF  NITRATE  NITROGEN:  AVERAGE  OF  ALL  SERIES,  UNIVERSITY  SOUTH  FARM,  1918 
Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6^  inches),  water-free  basis 


Rotation 

Date  of  sampling 

June  10 

June  17 

June  24 

July  2 

July  12 

Aug.  2 

Potatoes,  corn,  soybeans 
(alfalfa)  

68.48 

53.14 
41.  673 
36.60 

57.30 

50.90 
42.  183 
22.70 

65.8 

63.1 

28.8 
30.8 

34.1 

35.1 
29.3 
19.7 

20.6 

29.7 
17.1 
12.2 

25.5 

30.3 
20.3 
22.5 

Wheat  (red  clover),2  corn,  oats, 
clover  or  soybeans  

Corn,  corn,  oats,  clover  

Corn,  corn,  corn,  soybeans  

figure  represents  the  average  of  the  analyses  of  sixteen  or  more  plots 
unless  otherwise  indicated. 
2Seeded  on  residues  plots. 
'Average  of  the  analyses  of  eight  plots. 

The  demands  made  by  the  corn  crops  are  not  satisfied  in  the  poorer 
rotations  by  the  one  regular  legume  crop,  especially  the  soybean  crop. 
The  two  better  rotations  were  nearly  twice  as  high  in  nitrate  at  the 


1920] 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


55 


critical  periods  of  crop  growth  as  the  poorer  rotations,  in  spite  of  the 
fact  that  they  were  supporting  much  larger  crops. 

These  results  indicate  strongly  the  need  for  green-manure  crops 
in  rotation  systems.  Both  rotations  which  possess  them  showed  a 
marked  superiority  in  nitrate  production.  It  would  be  more  difficult, 
of  course,  to  introduce  sweet  clover  for  green-manure  purposes  into 
a  rotation  having  two  or  three  crops  of  corn  in  succession,  than  into 
a  rotation  where  oats  or  wheat  are  grown. 

These  results  do  not  require  extended  explanation.  It  is  ap- 
parent that  the  rotation  wheat,  corn,  oats,  and  clover,  with  a  green- 
manure  crop  seeded  in  the  wheat,  will  supply  the  nitrate  for  large 
crops,  without  the  use  of  stable  manure. 

CROP  SEQUENCE  AS  INFLUENCING  NITRATE  PRODUCTION 

The  opportunity  offered  by  these  data  to  study  the  effect  of  crop 
sequence  upon  nitrate  production  was  taken  advantage  of.  The  figures 
in  Table  25  show  to  a  certain  extent  the  influence  of  the  previous  crops, 
but  in  drawing  any  conclusions  from  them  it  should  be  borne  in  mind 
that  the  more  remote  crops  have  their  influence  as  well  but  in  a 
lesser  degree. 

The  data  actually  show  a  superiority  for  corn  following  wheat 
over  corn  following  potatoes.  The  reason  for  this  is  easily  traceable 
to  the  residues  plots  of  Series  300  and  directly  traceable  to  the  influ- 
ence of  the  green-manure  crop.  Both  sets  of  figures  include  the  in- 
fluence of  stable  manure,  and  even  tho  the  largest  amount  is  applied 
on  Series  400,  where  the  potatoes  grew,  the  residues  produced  the 
greater  amount  of  nitrate. 

Corn  after  corn  (1  year)  shows  the  anticipated  decrease  in  nitrate 
production,  and  the  same  may  be  said  of  corn  after  corn  (2  years). 
Even  rich  soils,  without  more  legumes  in  the  rotation,  cannot  attain 
the  same  high  nitrate-producing  efficiency  which  poor  soils,  well  sup- 
plied with  green,  active  organic  matter,  can  attain. 

These  data  support  the  well  established  belief  that  a  rotation 
devoted  too  continuously  to  one  crop  is  especially  hard  on  the  soil. 

TABLE  25. — 'INFLUENCE  OF  CROP  SEQUENCE  ON  PRODUCTION  OF  NITRATE  NITROGEN: 
CORN  SERIES,  UNIVERSITY  SOUTH  FARM,  1918 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6^  inches),  water-free  basisi 


Rota- 
tion 

Series 

Crop  sequence 

Date  of  sampling 

June  10 

June  17 

June  24 

July  2 

July  12 

Aug.  2 

SW. 
NW. 
NC. 

SC. 

300 
400 
800 

500 

Corn  after  wheat.  .  . 
Corn  after  potatoes 
Corn  after  corn 
(1  year)  

68.31 
63.04 

41.67 
31.98 

60.43 
55.58 

42.12 
19.19 

73.12 
51.41 

44.74 
31.32 

37.82 
32.16 

29.72 
13.43 

24.99 
15.72 

18.22 
9.99 

32.39 
23.82 

19.28 
27.35 

Corn  after  corn 
(2  years)  

'Each  figure  represents  the  average  of  the  analyses  of  eight  plots. 


56 


BULLETIN  No.  225 


[March, 


A  further  study  of  a  similar  nature  may  be  made  by  referring 
to  the  data  in  Table  26,  involving  rotations  in  which  soybeans  follow 
corn  (1  year),  corn  (3  years),  and  oats,  and  where  clover  follows  oats, 
which  have  been  preceded  by  two  years  of  corn.  The*  figures  for  soy- 
beans after  corn  (1  year)  and  after  oats,  in  the  two  good  rotations, 
show  increases  up  to  June  24  and  July  2,  while  in  the  poor  rotations 
only  slight  changes  occurred  from  June  10  to  August  2,  and  such 
changes  were  mostly  decreases. 

TABLE  26. — INFLUENCE  OP  CROP  SEQUENCE  ON  PRODUCTION  OF  NITRATE  NITROGEN: 
SOYBEAN-CLOVER  SERIES,  UNIVERSITY  SOUTH  FARM,  1918 

Pounds  per  acre  in  2  million  pounds  of  surface  soil  (about  0  to  6^3  inches),  water-free  basis  1 


Rota- 
tion 

Series 

Crop  sequence 

Date  of  sampling 

June  10 

June  17 

June  24 

•July  2f 

July  12 

Aug.  2 

NW. 

sw. 

NC. 

sc. 

100 
100 
600 
600 

Soybeans  after  corn 
Soybeans  after  oats 
Clover  after  oats  .  .  . 

73.99 
37.97 

59.23 
41.45 

80.62 
53.42 
23.01 

30.44 

36.24 
57.56 
26.97 

26.11 

25.64 
24.40 
15.19 

14.44 

29.89 
28.27 
21.28 

17.65 

Soybeans  after  corn 
(3  years)  

40.91 

26.44 

JEach  figure  represents  the  average  of  the  analyses  of  eight  plots. 

As  already  stated,  it  is  desirable  to  have  the  legume  crop  occur 
in  the  poorest  part  of  the  rotation  if  it  is  to  be  used  as  a  hay  or 
seed  crop. 

MOISTURE  DETERMINATIONS  ON  THE   SOUTH  FARM,   1918 

The  moisture  determinations  for  the  South  Farm  are  presented 
in  condensed  form  in  Tables  27  and  28,  having  been  averaged  for  whole 
plots.  All  the  figures  for  moisture  are  valuable  for  comparative  pur- 
poses (and  they  are  also  valuable  for  laboratory  studies  in  which  one 
wishes  to  duplicate  field  moisture  conditions  for  a  given  season). 
Nitrate  studies  which  are  accompanied  by  moisture  determinations 
furnish  data  on  the  minimum  and  maximum  limits  of  available  mois- 
ture for  the  bacteria  that  produce  nitrite  and  nitrate  under  natural 
conditions. 


1920] 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS 


57 


TABLE  27. — MOISTURE  CONTENT  OP  THE  SOIL,  SERIES  100  AND  400NW,  SERIES 
100  AND  300SW:  UNIVERSITY  SOUTH  FARM,  1918 

Tons  of  water  with  2  million  pounds  of  surface  soil  (about  0  to  "6%  inches),  water-free  basis 


Plot 

Treat- 
ment 

Date  of  sampling 

June  10 

June  17 

|  June  24 

July  2 

|  July  12 

Aug.  2 

ROTATION:  POTATOES.  CORN,  SOYBEANS,  AND  ALFALFA 

Series  100  NW 


146 

MLP  

294.5 

291.6 

277.7 

436.1 

329.3 

170.4 

149 

M  

293.7 

294.0 

281.6 

442.0 

304.7 

166.4 

150 

M  

281.6 

289.9 

269.3 

437.0 

311.5 

176.0 

153 

MLP  

253.0 

257.0 

248.0 

398.3 

277.3 

130.7 

Series  400  NW 


446 

MLP  

304.7 

279.7 

275.4 

341.3 

315.2 

192.5 

449 

M  

305.7 

289.1 

277.5 

351.7 

328.0 

198.9 

450 

M  

311.4 

289.2 

288.0 

354.8 

321.8 

203.2 

453 

MLP  

317.9 

287.2 

285.3 

360.5 

307.4 

220.7 

ROTATION:  WHEAT,  CORN,  OATS,  AND  CLOVER 
Series  100  SW 


166 

RLP  

258.6 

251.0 

254.6 

385.7 

267.0 

168.6 

169 

R  

236.0 

230.1 

239.8 

352.5 

232.3 

145.2 

170 

M  

234.3 

227.4 

223.7 

359.7 

233.9 

143.0 

173 

MLP  

249.9 

246.2 

243.7 

368.9 

248.5 

170.5 

Series  300  SW 


366 

RLP  

367.0 

351.3 

338.2 

397.2 

350.2 

241.2 

369 

R  

325.0 

316.0 

299.6 

353.7 

317.4 

200.4 

370 

M  

317.6 

315.0 

307.0 

351.5 

308.1 

201.3 

373 

MLP  

297.2 

300.8 

275.2 

324.4 

278.8 

137.8 

58 


BULLETIN  No.  225 


[March, 


TABLE  28. — MOISTURE  CONTENT  OF  THE  SOIL,  SERIES  500  AND  600SC,  SERIES  600 
AND  800NC:  UNIVERSITY  SOUTH  FARM,  1918 

Tons  of  water  with  2  million  pounds  of  surface  soil  (about  0  to  62/3  inches),  water-free  basis 


Plot 

Treat- 
ment 

Date  of  sampling 

June  10 

June  17 

June  24  |,   July  2 

July  12 

Aug.  2 

ROTATION:  CORN,  CORN,  CORN,  AND  SOYBEANS 
Series  500  SO 


566 

RP  

247.2 

224.3 

232.7 

281.2 

263.5 

187.5 

569 

R  

247.7 

226.2 

239.2 

277.5 

255.4 

180  7 

570 

M  

233.1 

209.5 

225.5 

269  2 

256.0 

178  7 

573 

MP.  . 

228.9 

197.1 

211.3 

264.9 

233.7 

163.2 

Series  600  SO 


666 

RP  

236.8 

215.5 

219.8 

374.4 

243.9 

140  8 

669 

R  

230  3 

242  8 

238  9 

404  0 

243  8 

133  5 

670 

M  

236.9 

217.5 

219.9 

367.7 

244.5 

139  5 

673 

MP  

229.0 

216.8 

221.4 

373.4 

240.2 

135.6 

ROTATION:  CORN,  CORN,  OATS,  AND  CLOVER 

Series  600  NO 


646 

RP  

161.3 

410.8 

263  0 

145  0 

649 

R  

146.4 

391.9 

256.6 

132.7 

650 

M  

148.1 

386.1 

240.3 

125  1 

653 

MP  

178.7 

425.6 

273.9 

159.2 

Series  800  NO 


846 

RP  

302  2 

284.4 

293.3 

316.9 

298  2 

202  3 

849 

R  

243.7 

263.5 

262.7 

280.2 

270.6 

182.9 

850 

M  

226.1 

235.5 

235.7 

253.6 

239.8 

159  5 

853 

MP  

224.4 

245.9 

219.4 

260.0 

266.3 

168.4 

1920]  NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  59 

SOME  IMPORTANT  FACTS  SHOWN  BY  DATA  FROM  UNI- 
VERSITY SOUTH  FARM 

The  soil  treatment  which  has  been  applied  to  the  University  South 
Farm  has  greatly  influenced  nitrate  production.  Green-manure  crops 
were  found  to  be  a  most  important  means  of  increasing  production. 
Both  red  clover  and  sweet  clover  were  responsible  for  large  increases. 
This  agrees  with  the  results  obtained  on  the  North  Farm  in  the  same 
year  (see  Table  16). 

Raw  rock  phosphate  was  responsible  for  increases  in  nitrate  pro- 
duction, especially  when  associated  with  active  organic  matter.  Its 
value  in  increasing  nitrates,  as  found  on  these  series  for  corn  in  the 
good  rotations,  amounted  to  18  to  32  pounds  per  acre.  If  a  value 
of  only  20  cents  per  pound  is  placed  upon  the  nitrate,  the  gain  in 
nitrate  due  to  phosphorus  is  equivalent  to  one-half  to  three-fourths 
the  cost  of  the  whole  application  of  raw  rock  phosphate  for  a  rotation. 

The  data  for  soybeans  show  an  increase  in  nitrate  production  of 
16  to  23  pounds  per  acre  up  to  June  24  even  tho  the  application  of 
raw  rock  phosphate  was  made  four  years  before  the  soybean  crop 
was  seeded  and  the  crop  occupies  the  poorest  part  of  the  four-year 
rotation. 

It  might  be  argued  that  the  effect  of  raw  rock  phosphate  on  nitrate 
production  is  indirect,  as  in  the  case  of  the  effect  of  limestone  on 
the  legume,  but  the  results  on  Series  300  indicate  that  it  is  direct; 
the  largest  figures  have  repeatedly  occurred  where  raw  rock  phosphate 
and  green  manure  have  been  used  together. 

These  data  lend  further  support  to  the  results  reported  in  Bulle- 
tin 190  (Soil  Bacteria  and  Phosphates)  on  rock  phosphate  furnishing 
the  base  calcium  for  nitrate  production.  Some  of  these  series  are 
acid,  and  only  where  raw  rock  phosphate  is  used  with  the  green  man- 
ure are  the  largest  amounts  of  nitrate  nitrogen  found. 

A  study  of  Tables  16  and  17  leads  one  to  question  the  quality  of 
the  manure  applied,  even  tho  the  quantities  were  large.  Unless  stable 
manure  is  kept  under  conditions  which  conserve  the  nitrogen  of  the 
urine,  it  is  poor  in  nitrogen  and  further  is  at  a  disadvantage  because 
the  nitrogen  compounds  left  are  less  rapid  in  their  decomposition  * 
than  those  lost.  It  is  now  recognized  that  green  materials  decompose 
faster  than  the  same  materials  once  cured  or  air-dried  even  for  a  short 
time.  While  green  crops,  especially  green  legumes,  will  undoubtedly 
decompose  faster  than  stable  manure  and  also  develop  more  acidity, 
the  differences  between  them  and  stable  manure  would  be  greatly 
decreased  by  a  better  handling  of  the  manure. 

The  kind  of  rotation  practiced  and  the  sequence  of  the  crops 
within  the  rotation  proved  to  be  important  factors  in  maintaining  all 
fields  in  a  high  state  of  nitrate  production.  These  must  be  given  more 
consideration  in  the  future.  They  bear  first  on  the  nitrogen  question, 
after  that  on  phosphorus  liberation. 


\ 

\ 


60  BULLETIN  No.  225  [March, 

CONCLUSIONS 

From  the  four  years'  work  reported  in  this  bulletin,  the  follow- 
ing conclusions  may  be  drawn: 

1.  INFLUENCE  OF  SOIL  TREATMENT  ON  NITRATE  PRODUCTION.— 
The  most  important  factor  in  increasing  nitrate  production  is  soil 
treatment.    Climatic  factors  control  the  course  of  nitrate  production, 
but  the  amount  of  production  is  dependent  upon  soil  treatment. 

Raw  rock  phosphate  is  an  important  factor  in  increasing  the 
amount  of  nitrate  produced,  and  in  good  rotations  the  effect  of  rock 
phosphate  is  much  greater  than  in  poor  rotations. 

The  complete  treatment  with  organic  matter,  phosphate,  and 
limestone  furnishes  the  largest  amount  of  nitrate  and  at  an  earlier 
period  than  organic  matter  and  limestone  or  organic  matter  alone. 
It  will  meet  the  needs  of  large  crop  yields  and  eliminate  the  necessity 
of  purchasing  commercial  nitrogen. 

2.  AVAILABILITY  OF  NITROGEN  OF  A  GREEN-MANURE  CROP  PLOWED 
UNDER  IN  SPRING,  FOR  THE  SUCCEEDING  CROP;    AND  COMPARISON  OF 
GREEN  AND  STABLE  MANURE. — The  question  whether  the  nitrogen  of 
red  clover  or  of  sweet  clover  plowed  under  in  April  or  May  furnishes 
nitrate  for  the  succeeding  crop  is  answered  affirmatively. 

Stable  manure  is  efficient  in  nitrate  production,  especially  when 
used  with  the  phosphate  and  limestone,  but  when  applied  as  it  was  in 
these  experiments  it  does  not  approach  the  rate  and  amount  of  pro- 
duction exhibited  by  the  green  sweet  clover  or  the  green  red  clover. 

Active  organic  matter  greatly  increases  the  amount  of  nitrate  in 
brown  silt  loam. 

3.  EFFECT  OF  DIFFERENT  CROPPING  SYSTEMS  ON  NITRATE  PRO- 
DUCTION.— Crop  rotations  in  which  legumes  are  used  as  green  manure 
and  in  which  the  crop  sequence  is  such  as  not  to  have  two  crops  in 
succession  that  are  heavy  feeders  on  nitrogen,  are  superior  for  nitrate 
production  to  rotations  in  which  these  points  are  ignored. 

4.  TIME  OF  YEAR  AT  WHICH  MAXIMUM  PRODUCTION  OF  NITRATE 
OCCURS. — With  corn  and  soybeans,  the  maximum  nitrate  production 
occurs  in  most  cases  in  June.    On  land  in  wheat  and  oats  the  largest 
production  is  found  in  May. 

5.  RELATIVE  RATES  OF  NITRATE  PRODUCTION  AT  DIFFERENT  SEA- 
SONS OF  THE  YEAR. — The  relative  seasonal  rates  of  nitrate  production 
arranged  according  to  the  seasons  are  as  follows: 

(a)  Late  spring  and  early  summer.     This  is  the  most  active 
period  of  production  and  accumulation.    During  this  period  optimum 
temperature  and  moisture  conditions  are  approached. 

(b)  Early  autumn.    A  second  active  period  occurs  frequently 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  ix  ILLINOIS  61 

in  the  autumn.     This  may  be  considered  a  second  approach  to  the 
/optimum  conditions  for  nitrate  production. 

(c)  Summer.     In  midsummer  little  nitrate  production  occurs 
unless  the  weather  is  cool  and  there  is  a  supply  of  available  moisture. 

(d)  Winter.    No  evidence  of  nitrate  production  has  been  found 
in /the  winter. 

f(D  FARM  PRACTICES  WHICH  REDUCE  THE  Loss  OF  NITROGEN  BY 
LEACHING. — Crop  residues  are  effective  in  preventing  the  loss  of  ni- 
trate which  results  from  leaching.  A  growing  crop  occupying  the  soil 
reduces  loss  by  leaching. 

7.  PERIODS  OF  GREATEST  NITROGEN  UTILIZATION. — The  period 
of  greatest  utilization  of  nitrate  by  corn,  as  judged  by  the  decreases 
found  in  the  nitrogen  supply  in  the  soil,  coincides  with  the  period 
of  greatest  visible  increase  in  growth,  which  occurs  usually  between 
June  25  and  July  15.  The  period  of  greatest  utilization  of  nitrate 
for  wheat  and  oats  is  earlier  in  the  season  than  for  corn,  coming 
usually  about  the  middle  of  May  or  early  in  June.  It  occurred  in 
these  studies  earlier  with  wheat  than  with  oats. 

The  period  of  greatest  utilization  of  nitrates,  as  well  as  the  rate 
and  amount  of  production,  is  directly  related  to  soil  treatment. 
In  these  studies,  the  properly  treated  plots  were  taking  in  more 
nitrate,  and  at  an  earlier  period,  than  those  receiving  poorer  treat- 
ment. The  recovery  of  efficiency  in  nitrate  production  occurred  at 
an  earlier  date  and  in  a  greater  degree  on  the  plots  receiving  the 
proper  soil  treatment. 


62  BULLETIN  No.  225  [March, 

APPENDIX 

METHODS  EMPLOYED  FOR  COLLECTING  SAMPLES,  AND  FOR  MAKING 
MOISTURE  AND  NITRATE  DETERMINATIONS 

Collection  of  Samples. — Two  or  more  field  samples  consisting  of  twelve  to 
sixteen  borings  each  were  taken  from  each  plot  or  half-plot,  as  necessary,  by 
means  of  a  soil  auger  or  soil  tube.  These  were  collected  in  four-inch  soil  pans 
and  thoroly  mixed  and  immediately  placed  in  glass  fruit  jars,  toluene  having  been 
added  to  the  jars  ahead  of  the  soil  when  samples  were  to  remain  over  a  few 
hours  before  drying.  The  jars  were  then  sealed  tightly;  this  is  essential  for 
active  soils  such  as  result  from  proper  soil  treatment.  Soils  should  never  be 
shipped  without  this  precaution. 

The  samples  represented  half  a  plot,  either  east  and  weet  or  north  and  south. 
One  nitrogen  determination  was  made  on  each  sample  and  the  results  averaged 
for  the  plot,  or  the  half-plot,  in  which  case  two  samples  were  taken  on  the 
half-plot. 

The  greatest  error  is  likely  to  result  from  sampling  a  cultivated  hill  crop. 
Sampling  drilled  crops,  such  as  oats,  wheat,  and  even  soybeans,  is  very  accurately 
done.  Where  cultivated  hill  crops  were  grown,  the  sampling  was  carried  out 
as  follows:  One  boring  was  taken  in  close  proximity  to  the  hill,  one  equidistant 
between  hills,  and  one  at  the  point  where  the  diagonals  from  the  hills  intersect 
each  other.  Five  such  sets  of  borings  were  obtained,  the  space  between  the  dif- 
ferent sets  being  about  equal.  The  sampling  was  made  in  such  a  manner  as  to 
include  the  half-plot.  When  the  small  grain  crops  had  reached  a  height  which 
made  it  impossible  to  use  soil  pans,  laboratory  stools  and  later  doth  aprons 
were  found  satisfactory  for  holding  the  samples.  Notes  were  taken  regarding 
condition  of  crop,  soil,  temperature,  and  rainfall. 

Moisture  Determinations. — One  hundred  grams  of  the  thoroly  mixed  sample 
was  placed  in  seamless  tin  weighing  boxes  and  dried  in  an  electric  oven  for  eight 
to  ten  hours  at  108°  C.  After  drying,  the  samples  were  weighed  and  transferred 
to  400-cc  shaker  bottles  for  further  work.  Moisture  is  reported  showing  tons 
of  water  with  2  million  pounds  of  water-free  soil. 

Nitrate  Method.- — To  the  oven-dried  samples  (70  to  80  grams),  which  had 
been  placed  in  400-ce  shaker  bottles,  was  added  300  cc.  of  hydrochloric  acid 
(approximately  0.2  percent),  and  the  samples  shaken  for  three  hours  in 
a  mechanical  shaker,  after  which  they  were  allowed  to  settle  over  night.  Care 
should  be  exercised  to  see  that  the  samples  are  acid.  (Breakage  of  bottles  may 
be  avoided  if  stoppers  are  loosened  where  carbonates  are  present.) 

A  large  number  of  substances  such  as  water,  alkalies,  alkaline  earths  and 
other  carbonates,  oxids,  neutral  salts,  and  various  acids  have  been  tried  for 
securing  an  extract,  but  the  results  have  shown  hydrochloric  acid  to  be  the  best 
defloceulating  and  settling  agent  as  well  as  a  superior  agent  in  assisting  in 
freeing  the  nitrate. 

An  aliquot  of  200  cc.  is  blown  off  into  a  800-cc.  Kjeldahl  flask,  5  to  6 
ec.  of  50-percent  sodium  hydroxid  is  added,  and  the  ammonia  is  removed  by 
boiling  down  to  almost  dryness.  It  is  desirable  to  add  150  cc.  of  nitrogen- 
free  distilled  water  and  run  down  a  second  time  where  organic  matter  is  high 
as  a  result  of  applications  of  manure  or  residues,  or  where  large  amounts 


NITROGEN  PRODUCTION  IN  FIELD  SOILS  IN  ILLINOIS  63 

of  ammonia  are  present.  The  aliquot  should  be  clear  of  solid  material,  but 
often  is  colored.  Filtration  is  seldom  necessary.  After  expelling  the  ammonia, 
200  cc.  of  nitrogen-free  distilled  water  is  added,  together  with  about  0.6  gram 
of  Devarda's  alloy,  and  the  content  of  the  flask  distilled  forty-five  minutes, 
air  and  heat  or  air  and  steam  being  used  as  desired.  The  ammonia  is  col- 
lected in  standard  sulfuric  acid  of  a  weak  strength  and  titrated  against  standard 
sodium  hydroxid  of  a  convenient  strength  to  simplify  the  calculations  for  parts 
per  million  or  pounds  per  acre.  Rosolic  acid  has  given  excellent  satisfaction 
as  the  indicator.  Methyl  red  is  also  usuable,  but  most  indicators  tested  were 
not  satisfactory. 

Trials  of  other  nitrate  methods  have  proved  the  superiority  and  reliability 
of  the  above  procedure  for  exactness  and  simplicity.  The  aluminium  reduc- 
tion, zinc-copper  couple,  iron  by  hydrogen  (90  percent),  titanous  sulfate  and 
phenol  disulfonic  acid  methods  have  been  tested  and  found  unsatisfactory. 
In  several  cases  from  three  to  seven  days  was  not  sufficient  to  reduce  the 
nitrate  by  the  aluminium  reduction  method,  while  thirty  minutes  completed 
the  reduction  by  the  use  of  Devarda's  alloy. 


UNIVERSITY  OF  ILLINOIS-URBANA 


